You might want to take a look at ICanAnimate from Kudlian Software.
http://www.kudlian.net/products/icananimate/
It's $49.95 bought online via Kagi. Not "low cost" I know, (sorry Chris) but it really is easy to use - very iMovie like. Also you can add blue-screened backgrounds and other cool stuff. I have used it with several groups of High School kids - and their tutors. They all loved it, and the results were great.
What's Next In The iLife Suite?