What Graphics cards do you have and if you're no longer using them would you be willing to sell them?
(Yes, I am playing with non Bitcoin, GPGPU based parrallel processing)
I only use GPU's for scrypt based coins (Litecoin etc). I use radeon 7950's. If you are buying then I'd advise you buy new and not second hand from another miner, oh and get the Saphire Vapour X ones. The reason is that they are running flat out 24/7 and the fans are not built for it. I keep a stock of replacement fans now and expect them to last 4-5 months in the spahires, and maybe 3 months from the other cards.
For bitcoin I use USB ASIC's now. Cheaper to run, more powerful AND have pretty blinking lights! I use headless raspberrypi's to control them.
It is an arms race though, hardware ages quickly in this game.