Take look at this airframe http://www.vimeo.com/4576567
Not pretty, but modular, parts are easily exchangable and the airframe is probably low cost.
One could probably make an electronics container in light foam instead of mounting the electronics to the outside of the front like it looks like this guy has done.
Exchangable payload modules could probably also be made.
Anyone know about a wing design that is similar to the one on the video?
Looks like the tail boom is in balsa and that the tail is a spare from another plane.
Note the rear mounted servos. Makes the tail detachable and allows for more weight in the front of the plane.