There is no accurate way to predict future values... it is dependent on so many variables. Is it limited production? Is it somewhat common but most were abused so ones in good condition are valuable? Etc. The surest way to lose money on a "collectable" is to buy something advertised as a "collectable"; they are usually manufactured in large numbers and people who buy them keep them pristine.

For current value, one can look at sold listings in ebay to see what they are selling for in a broad market or on CL for a more restricted market.