portable emulation

I wasn't sure where this should go, but because it's chiefly about computer tech and not images I decided to put it here.

'Kay, the thing is that I want a laptop or some kind of portable system that is just powerful enough to run a Super Nintendo, NES, or Gameboy Advance emulator smoothly, could be old, preferably compact (though I guess "old" and "compact" are not renowned bedfellows), with 2 or so USB ports to plug USB controllers into. 

Would this be possible?  As affordable as I'm hoping?  I know nothing.  Help me!

VisualBoyAdvance will require at least about a 800Mhz system for full frame rate

I sometimes see dropped frames with a 2Ghz machine, so that 800Mhz is far too low.

ZSNES will require a 400-500Mhz system for full frame rate.

I used to run zsnes on a 400Mhz system, and it was dropping frames constantly too.