I believe the expression you are saying or want to say is Bang for the bucks Meaning to get more for your money. Spot on means to do something perfectly . Like if you get a 100% correct on a test. Its spot on.

I'm not sure about anything to do with books, but a similar idiom would be "Right on the money." Hope this helps :)

You might be thinking of "bang on the nail" perhaps? This refers to hitting a nail with a hammer and placing the hammer just right (so you don't hit your finger!) There is also an expression "playing it by the book" which means doing something according to the rules, or in just the way it is supposed to be done. Hope that helps!