The short answer is...it depends. Not much help, eh?
Here is my long winded answer.
Probably the most common solution is just to attach/install a large hard drive in a computer (either your main/only desktop or some older "spare" desktop typically, but could be done with laptops as well) and then share that drive using Windows network folder share function. This is likely also the cheapest option (an internal "desktop" 4 TB drive will cost around $100 as will an external USB drive). This is cheap and relatively easy to do. The two main downsides are 1) that computer with the large "data" drive needs to be on all the time (or at least anytime you want to access the data on the drive) and 2) occasionally setting Windows shares and having all computers (in particular when running different versions of Windows) can be a little of pain (most of the time I have no issues with Windows networking functions, but on occasion it seems like to be difficult).
A solution that can be almost as cost efficient is to get a single drive NAS. You can get then for less than $200 (depends on how much storage you want and brand). The advantage of this is that only this device needs to be on all the time and will likely draw less power than a computer. They are generally pretty easy to setup...just plug in a network cable from your router and then follow the instructions on how to setup "share"/"volumes" or whatever that brand calls them. The main potential downside can be data recovery if the NAS bites the dust (but that that is not an issue since you religiously backup all your data, right?
Another option is basically a hybrid of the first two...and has already been mentioned. That would be to use a spare computer to run FreeNAS and install/attach a large hard drive to that computer running FreeNAS. This would be basically the same cost as the first option, but might be a bit more work as you would need to setup FreeNAS, which could range from being no problem (if you are fairly comfortable with computers) to a challenge/scary (if you are not very comfortable with computers beyond the basic type stuff and/or not too adventurous).
The next option that is an "expansion" of the 3rd one is to use an NAS that uses multiple drives with the drives setup in some redundant RAID array option (personally, I generally see no point in getting a two drive NAS only to set it up in RAID 0 or "concurrent" mode UNLESS you really need LOTS of storage...at lower capacities, you can generally get a single drive NAS with the same capacity as a dual drive NAS for a lot less). FWIW, this is the option that I like to use. This can vary in cost depending on how deep down the "rabbit hole" you want to go. A simple dual drive option with the two drives setup in RAID 1 (this is mirror...i.e. one drive is duplicated on the other drive) will cost somewhere in the $200s and up depending on how much storage you want. The advantage of this option is that you will now get a first level of backup with the RAID 1 2 drive NAS. In this scenario, if one of the two drives fails, the other one is still operational such that you can still get to your date. Now, note that I say that this is "first level of backup". You will still want to backup the data from the NAS to something else incase individual files get corrupted (such as maybe being hit with some ransomware) or accidentally deleted. If corrupted or deleted on one drive, it will be corrupted or deleted on the other. If you want to go further down the rabbit hole that just a dual drive RAID 1 NAS, then you get into 3 or more drive NAS devices that typically will be setup in some form of RAID 5 (or similar). This will be more expensive, but will give more capacity, be a little faster than RAID 1, and still give redundancy (i.e. that first level of backup). Personally, I have a 4 drive NAS and just got a 6 drive NAS. These just like single drive NAS devices are still fairly easy to setup the basic functionality, but you will also get other features as you step up to pricier versions. A variation of this is to use an existing computer to run FreeNAS but use multiple drives.
One last potential option is to hook up an external USB hard drive to your router. Many routers these days offer the ability to attach a hard drive to them to be shared across the network. This would cost basically the same as the first option...assuming your router offers this ability. Then you just need to go into the router settings to configure it (with some routers, it may just be a matter of plugging in the drive and it will show up in Windows).
I hope this helps and does not overwhelm.