the only thing wrong with baka's recommendation is that 2 r9 290s will go over the budget.

im running 3 r9 290's @ 800kh/s each on stock clocks @ around 74 degrees (static 73% fan speed)

i dont mind the noise, but i will say these stock fans are LOUD on the r9 290. i kinda like it... it's my little spaceship to the moon