Not cheap, but...

What makes this app better than the others I own (and thus worth more to me) is the FREE Mac app that integrates with it. I find it easy to make lists of spells for individual characters and sync them with my iPad. If the price bothers you, try the Mac app and see if you like it. The iPad app also works well with VoiceOver (important for having your device read out the details to you or everyone playing).
I would like to see more scope for nanaging spells while you are playing, but Im not sorry I bought this app.

Blind Programmer about SpellbookMaster, v1.5