I did a lesson with my elementary students that is entirely adaptable - and
probably more suitable for high school. Students covered a balloon with
paper mache and let it dry - we filled a water bottle with sand for weight, then
we attached the balloon to the top of the water bottle. The idea was based
on caricature drawings - a large head and a smaller body. You could add 3D
features to the balloon head with celluclay. You could really go anywhere with
this. If you are interested, I have a picture of this project. Although
it was done by a first grader - it came out nicely. High school students
could really go nuts with this. And...it's cheap.