USD $70 for mobo, $150 for cpu, $30 for ram, and a $200 video card will give you a 10k 3dmark06 system easy. And for another $200 video card you'll perform near 18k. Even with two cards you should have enough money left for HDD, Case, PSU, CDROM, Monitor, Keyboard, Mouse, Audio etc. (though if you already have any of them, its cheaper/easier just to use your old ones if they're doing their job just fine.)
That seems a little stretched dude. I mean I built a computer recently. I have a $110 mobo, $200 processor, $350 Video card, $122 ram, $90 HD, I'm only saying this because my comp only gets a 8995 on 3Dmark06 so the figures that you said couldn't get a 10k.
(specs, Asus M2Ne-SLI, AMD FX-62, XFX 8800 GTS extreme, Corsair 6400 800MHz (2x2048))