If someone wanted a bookmobile, they can be had for a LOT less. Here's one that recently went for $4,201:
It's newer and bigger, though it does have more miles and a non-working generator.
I bought mine for $3,830. It's bigger, has a working generator, is newer (than the craigslist bus), though it doesn't look as nice and did need some minor things done (cover for gen was broken, had to be painted due to pink paint scheme, had to remove wheelchair lift, etc.).
I'm sure it's worth the price, if you were needing a bookmobile to haul books around (are you a library, or a bookstore who wants a mobile storefront?), and it was the only one available. Me, I doubt I'd go over $10k for the perfect bookmobile (perfect as in recent year, low miles, bigger than what I have now, already has working gen and wired for power, lots of cargo space, bonus points if it already has minimal plumbing, etc.).