300 is a really tight budget for gaming pc and what ram do you have . you might be better looking at a good second hand machine to get more bang for bucks
AMD are releasing there next line up this year ie, graphics cards and cpus, so the prices you are looking at now will be a lot less later in the year, b4 xmas
wait till then to price your bits up then.
and get a gpu with 4gigs of memory as these will be just as cheap as 2 gigs if not the same price now.
play the waiting game and get more bang for your buck matey