This site advertises low prices and has several options but I have never personally dealt with them,
Windows 2000 server is not usually available on a low cost PC, because the software license alone will bring the cost beyond what is reasonable to pay. You may want to just get a PC with Windows 2000 installed and purchase a 5 user license of the server software later. Of course it depends on what version of server you want as to what the costs are. It would be good for you to install it from scratch anyway.