Please create two separate categories for books you "collect" and books you "own".
I think it makes more sense to have a separate category that only shows those books that you added purchase details to, and a separate category that either shows all books that I collected or books that I collected but haven't purchased. As for the money spent category, it can then only calculate the total money spent on purchased books, based on the added purchase details, rather than for every book collected.
This feels like a semantics issue. If you obtained a comic from a library/Hoopla/MU/DCUI, you are renting it - you don't own it. You can mark it read, which does not imply it was purchased. If you obtain a comic through gifts or "other" means, you can set the Purchase Price to $0.00.