I bought an R9 280X right before Christmas for $350. I've been mining with it on the side when I'm not gaming. With $350 now in the bank from Mining, I'm going to sell it on eBay for $350 (yes they're going for that) and then buy an R9 290x for $700. Right now, I'm really liking the new Powercolor. It has a great review on Techpowerup.
So that's going to be essentially $350 net for this R9 290X - then will mine with that and use it to fund another upgrade.
Now that's what I call a Best GPU for the $$ purchase...