Used gaming computers are widely available on Craigslist, eBay, and other online consumer-to-consumer sales sites. Local computer user groups may have for-sale bulletin boards (even real ones, made of cork). Classified ads in newspapers and "thrifty shopper" circulars are other places to look ...
I don't recommend taking a chance with random sellers on eBay or Craigslist--not when there are so many well-established merchants that offer proper warranties and return policies, as well as an assurance that the underlying Windows license is legitimate. OEM Windows software for new or refurbis...
Then in 1990 I found a Commodore Amiga for sale on a BBS newsgroup, a nerdy precursor to Craigslist that only technical people knew how to use. I traded $800 of my earnings from working at the gas station, for what would eventually be another six-figure quantity of computer experience. ...