I am pretty close to admitting that I really know nothing about site design, and am almost willing to pay someone to do it.
Do it. A good web designer is going to know things you will never be able to teach yourself. It is not just a matter of slapping some code together. A good website is designed utilizing concepts like User Experience, Usability, Color Balance, use of both positive and negative space, etc. Then someone writes the code to actually implement that design. One reason that many websites fail is because there is no unified plan. The business owner thinks they know what they want and just starts writing code, only to have to compromise their plans when they can't figure out how to do it.
If you know what you want, use MS Paint or Gimp or something to cobble together pieces of websites that you like so that you can show a developer. They should be easily able to transform it into a working web page.
You can expect to pay anywhere from $250 - $2000 per page, depending on what you want. The costs can go way higher if you think you want custom flash movies, for example. You will also be able to find people that claim they can do it for $50 a page or less. Don't do it. At a minimum it takes roughly 4-6 hours to put together a single page, including the time to agree on a design and discuss your needs, and taking the time to test the code on multiple browsers so that the page looks the same. $50 for 4-6 hours work, and have confidence that you are going to get a solid product? Won't happen.