Looking to sell my gaming pc. what's a good asking price?

case- apevia x-jupitor jr /w side window
cpu- intel quad core q6600(stepping g0) water cooled
mb- asus p5n32-e sli quad 680i
gpu- 2x evga 8800gt sli
ram- 4gigs corsair xms2 exteme
hdd- sony dvd/rw and sony dvd
hd- 320 gigs
psu- thermaltake tough power 750w
soundcard- creative x-fi xtremegamer
vista 64-bit

gpu is watercooled by coolermaster aquagate s1, has blue cold cathod neon lights, 2 thermaltake 180mm case fans /w blue lighting, lcd temp display /w fan speed control dial, professional wiring throughout.

its my understanding that evga has some kinda step up program. where you can trade the cards in on newer cards and pay the difference.?.? i've never used that so i'm guessing they are both still eligible. thanks in advance for any replies.