I really have no clue what cpu and gpu would sort of be the minimum to be able to play most games on high settings within reason of course, I wouldn't expect something like Crysis to be played on high but would expect it to run good on med or low. I guess I'm thinking something equal to or better than the Xbox one in terms of performance.
Been piecing together a gaming HTPC but I keep looking at the best specs on paper and it's driving the cost way up for stuff I don't really need. The gpu in particular is a hard one for me to choose wisely, it will be hooked up to a 1080p tv and I've noticed the specs on the cards I've been looking at go way beyond that resolution.
And then cpu, kind of been thinking about an i5, but wondering if an i3 would be any good for gaming. I'm basing it on the fact that I have an i3 laptop with integrated graphics and I am able to play Skyrim on low settings. Been with Intel for my entire PC experience and I have thought about AMD but I don;t know anything about them. But I wouldn't rule out getting an AMD for this machine, even tho I hear Intels are better for these little HTPC cases.
In today's games, I would go something at least an i3 + HD 7870. An i5 would be a much, much better performer though.
AMD is also a great option. The Athlon X4 750K/760K are great CPUs, and would probably last a bit longer than an i3 because of their quad core nature(albeit have less single core performance, though). An i5 would still be faster than an Athlon X4 760k, however.
These are pretty much your two options for M-ITX builds. AMD doesn't have M-ITX boards for AM3+, and has them only for FM2/FM2+.
Why does it have to be a htpc? Are you trying to make it replace the space of a console? Try this; http://pcpartpicker.com/part/cooler-master-case-rc902xbkkn1 -whilst it is not htpc sized, neither is it full or mid tower. That case supports atx, ATX, Micro ATX, Mini ITX and Thin Mini ITX, so it pretty much has you covered.
the problem isn't heat, amd chips don't really get any hotter than intel chips, it's the fact that the high end amd chips require a really strong power delivery system, it makes board design abit more complicated, and with that and the current am3+ m-itx boards (all none of them) not flying off the shelves noone is willing to invest the time/money into better or smaller boards... in short manufacture's are assholes
aaanywho, the question was cheapest so am3+ isn't even on the table, an i3 (if you want intel) or a 750k/760k (a good bit weaker, but cheaper and will still get the job done) will be plenty, you could pair that with a 7870/660/270/270x, a 7850 (or maybe even 650ti boost or (>) 7790) might still fit in your requirements, but i can't say for certain
"I guess I'm thinking something equal to or better than the Xbox one in terms of performance."
You could achieve this easily, as the xbox one runs most games at 720p not 1080p, which would make running games at high presets much easier. You could probably get an Athlon 750K/i3 and a HD 7850 and do fiine on Ultra @ 720p, which is around what the xbox one is playing at.
But, as you've said, you play at 1080p. Achieving High @ 1080p is a bit more difficult if your trying to make it as small as you are. I'd have to say go for an i5 and HD 7870/R9 270x, as you can't really get an AM3+ motherboard at that form factor, and the 750K really starts struggling once you pass the medium preset on most games @1080p.
P.S. Why are you so set on getting a HTPC form factor? It really limits what you can do with a rig. Not trying to be rude, it's just a thought. You could save a lot of money by getting a bigger case, as you could get an FX 6300 which is very cheap and plays games on high amazingly if paired with the correct gpu.
Thanks for the help guys. There is my build so far.I guess I can't really get away with cheeping out if I still want gaming performance and some future proofing. I did have a GTX650 in there but would saving $50 be worth the performance drop?
As for the case the one I picked is basically a tower turned on it's side and it could accept an ATB board. I just want something that looks minimal and matches my home theater components. It can also accept up to a 14" GPU. The only limitation is the cooler and since I won't be overclocking it's not a big deal. I'm also trying to keep it as quiet as possible.