TBH GPU mining is probally reached the end of its course...
ive personally got x3 7970 and they are hashing at over 600mh each .
wether you can invest in an asic that provides more returns on the $$$ and obviouisly less electricity cost.

why dont you try checking out btcguild they are selling block eruptor blades right now for US residence only.
and i believe soon they taking it international.
again i stress this is based on supply and demand.

the more people that want to mine will have the chance to get a stronger network.
and on the investment of purchasing an asic. consider if you have enough money to purchase one.
how reputable the company you are purchasing from are.

also what are your overheads for going through with this project.
I mean if your budget is 500$ then stick to 500$ then after this investment youll have an idea of what your return will be.
Better to bet on something you researched on compared to just throwing your money away....

Good luck