My setup:

Head Unit: Clarion DRX8675Z ($50.00 from a friend)
Amp: Alpine F-356 5-Channel 540watt Amp ($199.00 brand new)
Speakers: Infinity Kappa Components, 5.25" ($79.00)
Rears: DEI 6" Mid RearFill Speakers ($50.00)
Subs: Pioneer (2) 8" Sub Woofs in custom box ($100.00 friend)

Total system: $478.00.
Can't complain.

Oh, add like 6 hours of install time, interior removable, dynamat placing, etc.