There are a lot of computers that are coming onto the market from leases ending. Check Tiger Direct to get an idea of computers that you can buy with no operating system on them. Then get FreeDoshttp://www.freedos.org/
and you should be set. You should look for used computers locally, older computers with Win95 or 98 that can run DOS. You should be able to pick up old versions of MS-DOS at swaps also.