I would look for one that has an inverter (which will cost slightly more) and uses 410a as the refridgerant. The one I got is this one:
mini split air conditioner - ductless split system
it seemed to be the most efficient I could find. I've been happy with it so far.
It is only 120v so the install is not that hard for a DIY. You will still need someone to vacuum the lines, but craigslist is a great place to look.
Good luck!