I would advise something else. If you could pick up 6870 that would be a faster option then the 7770....it would be closer or a little over your budget but I think with rebates you can get it right for around 150..I have built a few rigs with that card and it does pretty well it can play bf3 with everything on high at 1680x1050. would compliment your system nicely.
Heres one for 140 with rebate: http://www.newegg.com/Product/Product.aspx?Item=N82E16814150521
also comes with 2 free games not too bad