The big stars I would say $40-50, the big dead stars may go for higher. I was just looking at Diana Hoppe's site and she had Earl Strickland signed cueballs for $50.
A ball signed by Buddy, Grady and Parica was $200 and sold, seeing how Buddy's health is not too good and he's getting on with age, and Grady passed recently, that would show you what a cueball with some known names would go for when they no longer can sign items.