This does not qualify as "Cheap" yet..., but Have you looked at the CubeSpawn project?
its an Open Hardware project I'm working on - Its 3 parts away from running
once it is running - I'll be using it to make parts for additional cubes - in time it should be able to make a lot of its own parts
I set out to use Arduino with it - and still will - but I'm focusing on the EMC version at the moment
see more here: http://cubespawn.com
And...
Its currently in a contest until the 30th of june as well
CubeSpawn, an Open Source FMS a vote would be nice 