Eh, I wouldn't normally do this because it just opens you up as a target, but I'm about to spend it all so whatever. I keep shooting myself in the foot every time Robby increases the price of books because I'm kind of OCD about buying 100 books at a time, but I also want to make sure I have enough money to fully upgrade my armor/weaspons if Robby decides to release an update.
(The Ancient Shield and Eagle Staff are just random drops I happen to have on me at the moment)I've never used the payvault. I don't really have anything against it, but it would be too easy for me to p2w, so I have a general rule for myself that I don't spend money on "upgrades". I think this is only 25 levels worth of money strictly from selling drops to other people for 50-55%, and after upgrading my armor from Beholder's to Skullcrusher's and selling the Beholder's set for only 55%.
I think I've used around 250 books so far (not counting the 100 I'm about to use), but I honestly don't remember and am too lazy to do the math. At least 100 of those were for 50k, and at least 100 of those were for 45k. I didn't really start making enough money off of drops to satisfy my requirement of having enough money to buy the next set of armor in order to start buying books in large enough quantities to satisfy the OCD until Black Bots were added (I did buy a set of 10 or 20 a couple times before Black Bots, I think).
I don't think I'm rich, but realize I'm no doing so bad.