I'm sure they're worth more than that if in mint-good condition. I wonder if the Rangers win the world series that might affect the value to. I'll tell you one thing for sure. This is a rotten thing to say but once Nolan Ryan passes away those cards are going to be worth a small fortune. If I were you I would hold on to those cards until that time comes. Why settle for $600 now when in 10 or so years it could be worth thousands...In the end its up to your friend. Try to persuade him not to sell.. Or if he's already made up his mind. Sell them to me!! Seriously If they are in good condition I'll give you much more than 6 bills depending on: Amount of cards, Card manufacturer, year, condition..