The band comes with the same one year warranty as the watch. If you are beyond that, you're generally responsible for replacement costs.
If you have an Apple Store nearby, I suggest you go in and talk to them in person. When I worked in retail, I always tried to do everything I could for a polite customer, one who asked rather than demanded.
Also, you might want to look at some other sources of Watch bands if the idea of paying Apple's prices is unpalatable. I've bought some very functional ones from Amazon for less than $20.