Building a new cpu with AMD processor

Ok, so first of all don't advice me to go with intel(Budget) and i just found out you have to specially look for CPU which have hyperthreading(I though all of i5 had hyperthreading).
So Yeah, I am a computer science student(1 year, lot of compiling ,rendering to come) and I just want to play modern games....I have a core 2 duo(since it came out) and it is slow for me now having used even i3.

Ok so the question is, I want a amd proccesor with suitable motherboard combination(mobo not too expensive please. maybe like 100$ max) SO I COULD PLAY ALL MODERN GAMES NOT IN HIGH SETTING BUT JUST BE ABLE TO PLAY. LIke if i play ac3 in my comp. it lags like hell...
I have a nvidia geforce gtx 430 (so an apu is neccesary maybe??)

Suggest from a-series or fx- series(doesn't matter if black edition or not).

Ty.