What I do for pricing is take ebay sold listings, find ones that are similar in condition, then do my adder value, then discount it 20%. The reason for the discount is the fees, supplies, time and effort for creating the listing, questions etc.
Adder value can be positive or negative. This is my personal estimate. For example, if I have a Post War item that has TMCC added, I will add, $50. If PS1, I subtract $100. If PS1
There can't be a book as it will be out of date as soon as data is started to be collected. I will uses older guides to gauge rarity. For example, if in 1995 a common item was printed as a value of $10, and the rare variation is at $30, I will keep that same ratio.