depends on what you call good. If you need everything $300 - $10,000 will get you a "good" computer.
If I had to guess, A mid range computer that will play DX10 games (just the box) about $400-$600.
I think your best bet is to set your budget and see what you can get for the $.
How much are you willing to spend?
What kind of games are you playing?
How long will this computer have to last you?