I have asked the same question here about every 2-3 years as I move onto other projects and eventually get pulled back to MAME machines and upgrading or building a new one. I had in the early days some Old AMD athlons running early MAME just fine. I had a E8400 Overclocked to 3.6 and (remember this is a MAME version from 5+ years ago) almost everything ran fine. War Gods was my Benchmark back then, along with Gauntlet Legends, both which ran very close to full speed on teh E8400 (but only when it was OC'ed). There where a couple of 3D games which did not (some flying bicycle game i forget the name of). I currently have a 2500 (none K version) which i bought here for $130(ish?) from a member who had quite a few for sale 2-3 years ago. Which if i remember right played most everything (again in the Version of mame 2-3 years ago). I have also built a small machine with an intel G3258 4 Pentium 3.2 (MB and CPU is about $100) a core 2 DUO which seems to handle pretty much any game in MAME quite well. This last one is my File server/Multi Media machine with a 5TB USB drive with MAME and emu's plugged in with a couple 360 gamepads. Most used machine in my house, streaming KODI to one of the TV's and MAME to another, would recommend this build if you are starting from scratch. But as most said, almost any machine made in the last 10 years will play 90% of mame games, some 3D and pretty new stuff maybe wont play full speed, but with all the games that do, you should find something to play. I have built a few Rasberry PI machines too.. there is not much they wont play either. Hit a 2nd hand store, they almost always have a few $50 PC.. unless they have something from the early to mid 90's still on the shelf you will be able to play most MAME stuff with anything they have. good luck and enjoy!