I finally called it quits on trying to do this cheap. After reading a lot of web pages and talking to a couple people at the Star Wars movie, I’ve placed an order for some Etymotic ER6i noise blocking in-the-ear speakers. They’re supposed to block 34 – 36 dB of outside noise, which is about 10 dB more than the foam earplugs that I wear when riding. They’ll be in in about a week, so I’ll post a review after I’ve tried them out.