I suspect you could acquire and scan every readily purchasable book for much less than $3k each. Scanhouse for instance charges $0.15 per page for regular unbound (disassembled) books, plus $0.25 for supervised OCR, plus another dollar if the formatting is especially complex; this comes out to maybe $200-300 for a typical book. Acquiring, shipping, and disposing of them all would of course cost more, but not thousands more.

The main cost of doing this would be the time - even if you bought up all the available scanning capacity it would probably take months. In the meantime your competition who just torrented everything would have more high-quality training data than you. There are probably also a fair number of books in libgen which are out of print and difficult to find used.

It's a tiny amount of data relatively speaking. Much more expensive per token than almost any data source imaginable