Maybe Graphics Problem In Australia

Hey guys got a techy problem for you here.

So i started playing ffxiv a bit a go and ran fine like 40 - 60 fps oon standard desktop now all a sudden its been dropping down to 25 fps and just kinda wondering what it could be and i think i know the problem prob my graphics now saying that and if it may be that or maybe its the heat here in QLD Australia here just wondering what a good graphics card that wouldnt cost me an arm and a leg for to upgrade

specs are Intel(R) Core(TM) i3-2120 CPU @ 3.30GHz, 3.30GHZ
RAM 8.00GB on 64 bit windows 7 Grapics AMD Radeib HD 6500 Series