How much could i get, for this on eBay?

ok, i got this book called "four perfect pebbles" and on the inside cover i got it signed in person named Marion Blumenthal Lazen, she was one of the authors of the book and shes the one in the story, its a holocaust story, its a true story about Marion during the holocaust because shes 1 of the survivors of the Holocaust, and since she signed my book the she wrote with another person, i thought it might be worth something, so can anyone give me an estimate price of the book with her signature in it?? the book is basically in mid-condition, (like it matters) so can anyone help?! thank you