Thanks for the feedback. I have been very busy with a grad project and have not been tuning in here as of late. An example of what I am looking for would be a 2 liter soda bottle rocket using water/air pressure that I build with both my Earth Science and Physical Science students. With the exception of tape most of the items going into this are free or very low cost.I teach HS by the way, about 180 students per year. My supply budget is $400. I used up most of that just buying a couple of sets of class pack mini solar car kits. Again thanks for all the info and I will look down the various avenues that have been pointed out.