How much is Charlie Brown worth?

I'm sorry to say, Charlie Brown books from the late 1970s are not worth much. Many of them are still in print. (If they were out of print, then the books from the 1970s would likely be worth more.) Also, so many millions of copies of these books were sold, they aren't very rare and are readily available in used book stores, thrift store, and online. You could try selling yours at a used book store or online (Amazon and eBay), but I saw a Charlie Brown book from 1976 selling for $.01 on Amazon. Good luck!