How do I find out how much an autographed baseball is worth?

Does anyone have any idea how much an autographed 1988 Mets baseball is worth? Or how to get it appraised without spending too much? I don't have the COA any longer. The signatures I can read off the ball are: Jeff Innis, Kevin Elster, Barry Lyons, Gary Carter, David Cone, Mookie Wilson, Keith Hernandez, Randy Myers, Wally Backman, Bob Ojeda, Gene Walter, Terry Leach, Mel Stottlemyre - there's about 28 signatures in total. Any advice on how to make some money off this ball would be greatly appreciated. Thanks.