Will Smith once turned down the role to play Neo in "The Matrix." The part went to Keanu Reeves. Will Smith instead chose to star as a cowboy in the blockbuster failure "The Wild Wild West."

Kevin Costner also once turned down the role to play Andy Dufresne in "Shawshank Redemption." The part went to Tim Robbins. Kevin Costner instead chose to star as the Mariner in the blockbuster failure "Waterworld."

Based on the information above, what is one of the most relevant costs both Will Smith and Kevin Costner should consider when evaluating future movie projects?