Okay, so I'm thinking about building a Gaming PC with some Christmas $$$

I was pretty much just going to follow the latest video I saw on this site for a $350 build, but I was wondering something: Why use the A10- 5800k APU instead of a cheaper A8 or A6, the A6 is way cheaper, how much would it affect the quality of games? The main games i'm playing are Starcraft 2, Diablo, and Dota 2, does anyone know how well these processors run these games? 

Also, I figured I could get some better deals for a case/ hard drive if I tried to find some used, does anyone have any advice for where to find good used parts/ what parts I should buy used and which I should just get new?

Those games (maybe not DOTA 2) take vary little graphics power. But you should get the A10. http://www.tomshardware.com/reviews/a10-5800k-a8-5600k-a6-5400k,3224-18.html