You can totally copy the spells and then sell the spellbook. The cost might vary based on the buyer and how common the spells are.The corollary here is if you give out the spellbook, can the PCs sell it and for how much? Can the PC wizard copy the spells from the book into his and then sell the spellbook?
You can totally copy the spells and then sell the spellbook. The cost might vary based on the buyer and how common the spells are.
A 1st level wizard with only a handful of spells might pay quite a lot of money (assuming he has plenty of it) for a book with a number of 1st and 2nd level spells. That same spellbook might be worth very little to a wizard of 5th level or high who might only find a couple of additional spells. A book containing high level spells, especially those of 6th level or higher will probably always go for a high amount. How much is probably campaign dependent.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.