Can't you also say: C'est combien, un livre?
Yes, that is something you could say, though it is less academic than the proposed structure, that you would use in writing.
Could you use the verb "valoir"? So it would be "Combien vaut un livre?"?
mais oui, no problem with that.
Note: "valoir" is the same family as "valeur" (value). Therefore, in certain context, "valoir" may not related to a sum of money but to a "worth" if you see what I mean?
Ah ok so it would be better for a sentence like "How much is that book worth to you?" rather than one purely about money. Think I've got that, thanks!
We understand each other...
Why is the generic structure "combien ca coute" for how much does that cost, and "combien coute un livre" when asking about a specific item?
I think you answered your own question in the asking?