Fortune = a large amount of money Absolute = 100% (but in this case, adds emphasis) It is worth a very large amount of money. Michelle https://www.italki.com/michelle

I understand that It is very, very valuable.

It's a joke. He's making a joke about books that are more expensive if signed by the author, as there are usually few of these, making them collectible. Here, he has just said previously in the movie, that the author signed many, many copies, so actually in the case of this book, an unsigned one is rare and valuable.

https://www.dictionary.com/browse/absolute?s=t

It is very, very valuable!