What is it worth? 1965 Chicago Bears football

How do I get a good appraisal on something like this?

It was a ball given out at a end of year "thank you "function,
thrown by the club. It is a regulation ball that has stamped on it
"1965 Chicago Bears". It is signed by most of the team, heck it
may be the whole team but the some of the signatures are hard to read.

Here are the ones I could make out. Also, does it matter that this was
Gale Sayer's rookie year?

* RB/E Jon Arnett
* DE Doug Atkins
* QB Rudy Bukich
* RB Ronnie Bull
* LB Dick Butkus
* G/T Jim Cadile
* DT/DE/G Dick Evey
* LB Joe Fortunato
* DB Larry Glueck
* WR Dick Gordon
* P Bobby Joe Green
* WR Jim Jones
* G/DT/T Stan Jones
* RB Ralph Kurek
* LB/K/C Roger LeClerc
* T Dick Leeuwenburg
* DT Earl Leggett
* FB/RB Joe Marconi
* WR/HB Johnny Morris
* DE Ed O'Bradovich
* LB Jim Purnell
* C Mike Pyle
* LB Mike Reilly
* RB Gale Sayers
* DT/G George Seals
* DB/WR Ron Smith
* DB Rosey Taylor