Hey, first of all, if you could get good used ones(used by gamers) in either craigslist or ebay, go for it. I got mine used for $200 and mines at 800kh/s. And also just buy powered extender cables to manage heat and excess current on the board.
GPUs good to use:
5970 - 800 Kh/s
6990 - 800 Kh/s
7950 - 780 Kh/s
R290x (obviously it's brand new) - 800+ Kh/s
And get a good PSU. Don't mind the power bills, because if you do, it would be late to have one and difficulty on most coins will soar.
P.S.
You could resell those stuffs to some gamers later(at the same price you got them).
GPUs good to use:
5970 - 800 Kh/s
6990 - 800 Kh/s
7950 - 780 Kh/s
R290x (obviously it's brand new) - 800+ Kh/s
And get a good PSU. Don't mind the power bills, because if you do, it would be late to have one and difficulty on most coins will soar.
P.S.
You could resell those stuffs to some gamers later(at the same price you got them).