I believe there is a table in the Corvette Black Book. I will check mine when I have a chance. It is a table by year and broke up into 3 (I think) conditions (like fair, good and show quality). Mine is a 2008 version so getting a bit old but I am pretty sure that's where I found suggested values last time I looked.
In case anyone checked and found out I was wrong about the pricing tables being in the black book I am trying to find it still. now I want to know where I have that table!