Curious as to what you mean by 'legacy' 64-bit. I take it my old Compaq desktop, with the Athlon 64 X2 and DDR1 RAM, falls into this category, yes? 
(And at present, she's still running sweetly...)
As for 64-bit Pups, there's several out now. Tahr64; Xenialpup64; Artfulpup64.....even got folks working on BionicPup64 (based on 'Bionic' Beaver,which, as I understand it, is still several months away from release yet!) This will, of course, be the next LTS release.
Then there's Slacko 64 6.9.9.9, which will join the 7-series, once the final round of bug-testing is out of the way. Plus a few 64-bit 'specials' in BarryK's 'Quirky' series. So there's a fair selection to choose from.
And don't forget.....every one of these is UEFI-capable now.
Yet I still find the 32-bit Pups absolutely fly on this thing...
Mike. 
By 'legacy' in 2017, am speaking of mid to late Intel Socket 775 (especially those with DDR3 RAM) & AMD equivalents, or much any computer truly designed to run Windows Vista (not to be confused with Vista shipped on XP certified hardware
). Most have which has been recently retired from the corporate IT environment, mid to large sized business, education, etc, as many has purchased new fleets of computers & when new ones are installed, all of the old goes to the highest bidder. Who then in turn cleans these up, tests for defects, using the few broken ones to salvage parts to fix most of the good ones, and that equals a great deal on eBay for a PC that's Bitlocker capable, of which there's also a Linux workaround for. One of my best deals was snagging a Optiplex 780 DT edition (smaller than the MT), with a Intel Core2Quad 9650, Windows 7 Pro preinstalled with matching COA & recovery partition, plus having 2GB of DDR3 RAM (that I'd later upgrade to it's max of 16GB), all for a total of $114 shipped. The CPU alone fetches up to $150 on eBay used ($69-100 average), depending on condition (much higher if rare brand new sealed box), plus having 7 Pro was sweet also, which was an appropriate OS for company usage.
Many of the rest of the same model shipped with the Core2Duo E8400 instead for $79-119, so after digging through several pages & finding the one I did & seen only 3 out of 1,000 were left, acted fast by clicking the 'Buy it Now' tab & have never regretted purchase. 
By W10 standards, even some of these 10-12 old computers doesn't support the OS (nor W8.1) w/out a hardware upgrade, often a low cost CPU or GPU one. To get the best out of mainstream distros such as Ubuntu, or any distro that's graphic heavy, one needs more than some ATI 3xxx/4xxx series card. That's why I splurged a whopping $20 on a GPU that shipped with the XPS 8700 in 2013 in the 1GB GDDR5 Dell OEM Radeon 7570 for my latest project in another Topic, a GPU which I now own four of, needs no extra power & many ships with a low profile bracket, perfect for upgrading decade old business desktops with a PCIe slot, even 1st gen standard (PCIe version 1). Today's standard is PCIe 3.0, with 4.0 coming. Most of these legacy desktops I own has PCIe 2.0 (or 2.1).
As far as 'affordability' goes, there was once a time when I felt the same way. Rather than resigning to the idea that I'd always be outpowered on these Tech forums & for my personal needs, I created a savings plan that made it easy to save a minimum of $50/month. I stopped looking for excuses to go out just to stop at the local bakery 3-4 times weekly to have a couple of donuts & coffee that would be pooped out anyway and as an added benefit, lost weight also. Plus stopped paying $1 for a soda everywhere, instead stocking up when on a deal like 3-4 12 packs for $10-12 & started carrying a cooler when on the go with a few inside. also cut dining out to just one time per month (rather than 2-3), all of that equates a lot of saved cash. In my first month, had nearly $80 in my stash that I would had otherwise blown & while I haven't been able to match that every month, it was a beginning, one that would first in 2013 make my XPS 8700 my best (& last
) OEM PC. Later would go on to performing my first build with all new components in this very section of the Forum, then another upon another (both AMD & Intel builds), plus picking up a few decent 'legacy PC's', of which I termed above, not to be confused with ancient. 
While it may not be possible for everyone to have the same success I've had, on the other hand others has done even better, yet most anyone can commit to a decent $150 computer. There's some organizations that gives these away to those in need, or sometimes a friend or relative will do the same. I cannot begin to count the number of computers, both desktops & notebooks that I've given to friends & neighbors in need, most were given to me for work performed. Notably, a barely two year old Dell Inspiron to a 11 year old girl who later wanted Peppermint Linux to have along with her two friends the same OS, plus gave her mother a still overall great shape Optiplex 740 for ner need, to look for employment & in no time, found gainful employment. So if one cannot afford, there's no harm in swallowing some of that pride & ask around. Note that neither the mother nor daughter asked me of anything, they're my neighbors & seen them walking regular, looking down & out and I asked if they needed food or any help that I could provide or lead to resources.
I allowed both in, as it was cold & they explained the situation (the husband/father abandoned both), fortunately the home was paid off shortly afterwards, so the first priority was a job. Which via my donation, she found two jobs, accepted the first, then later declined & accepted a better one. Then I hooked the family up with resources to help with home repairs for those who qualified, which would have cost more than $10K out of pocket. Point being, both came out to the good, plus the young girl, now around 13-14 years old, is a far better Linux user than myself. 
So if one cannot truly afford a computer (& by that, I mean 'truly'), there's resources available, many times just by asking relatives, friends, neighbors or as last resort, an organization that 're-homes' otherwise unwanted computers that's donated. Offer to do some work if needed, or better yet, if someone outright gives one a computer, example in the fall, go rake their leaves while they're away to express thanks. Or in the season, mow their yard or shovel their driveway of snow, any meaningful gesture of thanks is better than none if able to perform work. More often than not, many 'have nots' are those that 'want not'. 
As to the older 32 bit computers that's still running, as long as the owner(s) desires & distros are available, it's OK to run any 32 bit distro that it's capable of. In fact, I met a person just a 5-6 weeks back who was still using one of my first notebooks owned, a Dell Latitude C640 (a true legacy computer) & running the non-PAE version of Ubuntu 12.04, a distro that wasn't openly advertised, nor am I certain that it was official. Yet it was in plain sight if one looked around, Ubuntu's answer to Linux Mint 13 LTS that ran on non-PAE computers. My first thought was how he remained secure, oddly, even though Ubuntu was no longer updating the OS, the browser (Firefox ESR) was up to date, along with needed plugins, plus he added a few PPA's to get extra updates. This man was still performing transactions on the computer, needless to say, I gave him an Optiplex 760 that was given to me & I had cleaned up. When I seen him a couple of weeks back & asked him was it still running good, he had installed Ubuntu 16.04 LTS (64 bit) on there, totally replacing Windows 7 Pro.
Giving back to my local community is important to me, not only re-homing computers when possible, also donating to the local food bank by donating both non-perishables & cash, as well as an occasional repair of one's computer when asked to. Although all of these folks are truly needy, are getting some type of assistance. As for freeloaders (those working & simply wants a free ride), I ran them off long ago & flagged their phone numbers to show as scammers (on my phone only), as I don't have the time nor desire to deal with those whom thinks the World owes them a living. 
However, I won't openly give a 32 bit computer to anyone, if one comes my way, is donated to the local Hospice store after installing Linux Mint Xfce (am not playing a part of spreading XP Malware around), where those looking for those types can find a wide variety at low cost, in the $25-50 range, as well as finding components from scrap computers for repair. That way, I can get rid of these w/out adding to landfill waste nor liability & hopefully most will use the Mint install performed after nuking the drive with DBAN (7 pass NSA wipe). 
Cat
Edited by cat1092, 15 December 2017 - 05:51 AM.