I think I have the very idea for the next challenge which should be possible and inexpensive for most.
I propose wire frame models but no inanimate objects, so there will be allowed a motor with a set of gears and of course a battery pack but other than that everything else about the model must be wire which will be brazed, soldered, spot welded, tied to form the model and it must move in some way. For example if you build a model car it must move along the ground.
Thoughts?