I'd like to see how well these guys could do with the good ole COX TD .049s.
Prepping for the event would take students through some very basic engine "detailing" and the very limited power adds a lot of spice to the design exercise. They can go fast enough to be fun and the overall cost to campaign one of these is about as cheap as it gets. You could have 2 planes ready to run for about the same amount of investment as one .40 sized racer.
Another idea is to base an event on the very inexpensive ASP .12s. You can use basically the same weight building methods and equipment as you would for the .049 class and these planes will do 130 mph.