Personalized signature of "Holes" by Louis Sachar

I have a copy of "Holes" signed by Louis Sachar that I recieved when he came to my school in 2000. The signature is personalized ( i know that tends to make the value less), but i don't have any questions of its authenticity (as I was there when he signed it). Great guy, by the way. The book itself is in great condition when it comes to certain aspects such as,  no folded pages, no marks or dents, that sort of thing; Unfortunately, I left it stored in a box that was in a basement for many years. The basement has become infested with mold and there is some minor mold on some of the pages. It doesn't seem to be permanent though, as a lot of it blew off ( like dust). I'm not an expert though and I don't know if this can be fixed or not. I'm sorry for the lack of quality in the pictures, I don't own a camera and my phone is old. I'm just looking to get a general or rough estimate to how much this would be worth if I were to sell it.  If there's anything I can do to help value, please feel free to contact me. Thank you.