You hinted about an AR, you mentioned .308 and AR15 at the same time. The .308 is on the AR10 platform which is much larger than the AR15, they're not interchangeable. I'm a big fan of building your own AR if that's what you want, and if you want to hunt with one do it. There are a lot of options for the ar15 platform, like the 6.8SPC, 6.5 Grendel, or even the .25WSSM. If you build it yourself you can definately do it for under 1k, my 18 year old son just built one for about $800.