At the other end of the price spectrum, I am going to try the HobbyKing outrunner in the e-Supra I am building:
I have had good success with an NTM (HK) 3548 900KV motor in a 2100g glider, but the motor is a bit heavier than I want. The 3540 600KV motor is a bit lighter (146g), and the lower KV should allow a bigger prop. And for $17.59 it is about 1/15 the cost of most of the options discussed here.
While the bigger props gearbox set-ups allow might be nice, prop efficiency does not always get better at the lower rpm required. Low Re effects on the small blades at low rpm can hurt the prop efficiency. These tests by Selig et al at UIUC, while limited in rpm range and prop types, show there is definitely an rpm you don't want to go below for most props - fortunately it looks like 3000rpm+ is OK for many props.