Logisys sells a 480W power supply for $13.
Newegg.com - LOGISYS Computer PS480D 480W ATX12V Power Supply
you can go very cheap, I do not know of anybody that would recommend using anything like that. I can go cheap but probably around $300. for a build because you need decent parts that will last
Power supply; about $35 to $40
Same for a case...$35 to $40
4 gb memory: $20.
dvd/cd burner: $20
The main board and cpu can vary but I'd think $125 to $175 range
The hard drive is a tough one these days, a 500gb can be had for $75. (unless you know someone with a cloud service that changes out hard drives a lot and asks $40 for a 500gb with warranty left on it.)I got lucky with that