I have had luck before with Insteon in remote buildings by using the boosters (
http://www.smarthome.com/insteon-2992-222-range-extender.html )outside and facing each other.
NOTE: they're not rated for outdoor use, but I had outlets placed about 1 foot under the eves of the house and storage building that faced each other and plugged in the boosters. In the three years I had that in place, it never failed. The building and the house were about 110 feet apart. The building had 240V (split-phase 120v) so I ensured that the house booster and the building booster were on different phases. It takes a little bit of work and planning, but you can make it work reliably if you have a clear line-of-sight. I have a friend that has extended Insteon about 400 feet from his house to a pier on a lake. There is a Gazebo/Pavilion about half-way and he used that as a repeater-point using a method similar to what I describe above.
The old boosters had stubby external antennas, seeing that it's 915MHz, you could also get creative with modified antennas, obviously voiding your warranty in the process, but hey, that's half the fun, right??? I think the new ones only have internal antennas, still though, could be fun to play around. I don't have a need for that any longer as my new property is quite small...
Terry