If you want to make a bit of a project out of this, you could power the wifi router/cable modem with solar power. A quick search turns up this page with a bit of help:
http://www.solar4power.com/solar-pow...ing.html#loads. I would also definitley recommend using a directional wifi antenna, not just a "high power" antenna. 1500 feet may be in the official specs for that antenna, but with wifi, unless you are in a desert without any obstructions, expect like 1/2 the maximum rated range.