OEM versions are cheapest........and I'd guess online would be cheaper than in a local pc store. I couldn't recommend where specifically since I'm in Ireland and doubt my local stores would suit ;)
dicecca112 wrote:find someone at a large college. Usually you can get it anywhere from 15-50$ for XP Pro
Absolutely, and if that doesn't work you'd probably be able to find one on a sufficiently large computer forum since they tend to be populated by exactly that demographic.