When testing on the ground I can walk about 1000 feet away before the signal becomes messed up. This is with trees and all kinds of obstacles in the way. In the air I've haven't had a chance to fly that far away but the video remains crystal clear the majority of the time and without a doubt wouldn't have any problems going further. A guy with the same transmitter as me was able to fly 35,600 feet in the air at a line of site distance of 13 miles.

[youtube]http://www.youtube.com/watch?v=QCDPWYM7T-U[/youtube]

This was with a directional antenna. The most cost efficient way to get that kind of range would probably be to buy something like this. Here is the antenna the guy in the video used. Note that this is for 2.4ghz stuff and won't work for anything else.

You would run out of controller range long before you ran out of video range with that. A 1 watt 2.4ghz transmitter and a standard receiver without a huge antenna should get you really far. Probably further than the range of the average 2.4ghz controller transmitter range since those transmitters have an output of less than 1 watt.