Are you familiar with "Cracker Barrel" restaurants? You'll find them all along the Interstate.
They have a program where you "buy" the tapes or CDs. But you can turn them back in at any Cracker Barrel location and get all but $3.00 back. The selection isn't always that great, but sometimes you get lucky.
There aren't any in Vermont, but here's their list of locations in New York. Seems like you should hit at least one.
http://www.crackerbarrel.com/location.cfm?state=NY
I love Cracker Barrel! I don't know if that'd work, but I'll keep it in mind.
The library here also has a good selection, at least of classics, Harry Potter, and LOTR. Not much else...but not bad. ;-) So that might be an option. I want to discuss it a little with Margaret. The only thing that worries me a bit is the chance of damage on a long trip like this.