Unfortunately, publishers neither give companies like Roll20 a cut of their book sales nor do they provide them with ready to use data for use on their gaming platform. Roll20 staff had to make, for example, the PHB and other D&D compendiums here. So naturally they charge for them. I know it's annoying from the player perspective. But think of it like buying anything else in a different format. If you own a vinyl album or CD of an album, iTunes doesn't give you the digital version for free or at a discount. Same thing with ebooks.
