$400 USD?

$119.99 - AMD Phenom II X3 720 (Could opt for the Phenom II X2 550)
$84.99 - Gigabyte GA-MA770T-UD3P
$89.99 - Corsair 550VX ($20 Mail in Rebate)
$109.99 - XFX HD4850 512mb


That takes you to $403 without the $20 MIR, so, in about 10 weeks when you actually get that rebate, it will equate to $383!

Seriously, $400 is not much to work with.