Yeah, the USPS has the 'media rate', so why not take one of the book boxes to a post office to get an idea of how much it will cost to send a box of books, then check the cost of shipping a lighter weight box through UPS? It may be cheaper to use UPS for some lighter weight boxes and take the heavier boxes in the van.
I used the rating thing on usps.com...some of my heavier book boxes will cost up to fifteen dollars each. I suppose it's cheaper than replacing 'em, but it adds up fast.
Ungh...wish the van hadn't needed so many repairs!
Guess I'll just hafta see how efficiently I can pack the van, for one.