If you're selling your old consoles to buy a new one, I'd say don't bother. The going rate to buy a gamecube at a pawn shop is about $30, and $40 or $50 for a PS2 or Xbox. To buy. If you were selling them one you'd probably get $10 or $15 for each of them, not nearly enough to buy a $300 PS3.
Keep your old systems, selling them is simply not worth it for the pittance you'll be paid for them.
Keep your old systems, selling them is simply not worth it for the pittance you'll be paid for them.