Thanks, everyone. I don't mind paying for a book I'm going to read Right Now, but I do object to paying over $20 for an ebook that I read for fun. I thought it might have been a mistake, that it didn't get changed when the other stores lowered them (competitive pricing), but it sounds like it's not unusual for them to be the odd one out.
I did check my library and they only have the audio version. Either my library does not have much ebook traffic or it's not the kind of traffic that checks out the books I like.
Thanks for all the replies!

The earlier books in the series are all less than $9, so I'll just wait until the next one comes out and then find a nice big coupon to use on this one.