Ok, I'm going to get started experimenting this week.

Here's what I'll do: I'll build the rocket plane (design is almost done), then I'll test it out with some sugar rockets using the end-burner technique. If that doesn't work, I might try ammonium perchlorate fuel - there are some "formulas" online, and it looks like you can buy the components relatively easily.

The beauty of the internet (and Youtube) is you don't always have to experiment much - there is usually already someone who has.