Yea they are cheap but not bad little things. Make sure you pick up some good thermal paste then if you don't have it already.
Speaking of the Pentium G3258 I actually already own one. Newegg gave me a motherboard to review and I used that CPU to do it. Seems I have got the worst CPU so far though. I only managed 3.9Ghz max. Some others managed as high as 4.2Ghz on stock voltage, and one guy is claiming to do 4.5Ghz with a slight boost. The problem is some of them, like mine and the guy who stopped at 4.2Ghz can't be overclocked any more regardless of voltage used. I increased the power by 30% and it still wouldn't hit 4Ghz stable.
Anyways, assuming you buy one and hit 3.9Ghz at a minimum, in some games you would actually get better performance than the AMD 6300. It depends on how well threaded the games are. While other games will be faster on the AMD 6300. I tested the one I got against an Intel i3 CPU, and the results are similar. My brother now uses the G3258 as his CPU in his computer, because he gets better performance in games like Skyrim. However, his performance for general use like web pages and such is down noticeably.
So that Pentium chip is a possible choice, but honestly the AMD 6300 would give better performance in newer games and all around general performance.