Playing CS:S with low detail and rolled back Direct X

My goal is to build the cheapest build I can possibly buy but still play CS 1.6 and Source since these are pretty much the only games I play. From what I can tell onboard graphics are going to have to be it if I am going to keep this as cheap as I want to.

I have read about people lowering the direct X version in the console of CS source ,which should help out a lot of people besides myself, and getting 40fps (unspecified res) with a 6100 onboard graphics chip. I was looking at a 780G which might be a little better.

I'm going to look and see if I can't find benchmarks of CS:S (HL2) with lowest settings in a high res (1600x1200 is what I prefer to play in) maybe toms charts have it. But I these charts won't account for any gain in fps caused my rolling back the direct x version being used. My goal is to be able to play CS:S (since 1.6 is easily conquered) in 1600 resolution in low settings with rolled back direct X and get 70fps and keep price as low as possible.

Any advice is much appreciated.