I think that the best option for you is something like BlackArrow Prospero X1, it's a 100 Gh standalone unit, come with it's own psu, and power efficence is arround 1w/gh , about the price, it depends on the model, you can find pretty cheap units without LCD, with LCD become more expensive, if you want i have one to sell, but i'm in Spain, so i don't know if you will be interested