Two words: model rockets. You can get a starter set for $20-$30 that comes with everything you'll need. Fun and educational.
My first place to look would be here:
www.estesrockets.com
A couple other sites:
www.ehobbies.com www.publicmissiles.com
Just as long as you don't launch a relatively heavy Death Star rocket on a B engine... not that I know anybody who did that... ::whistles innocently::