Give your 11 year old ten dollars for weeding the garden. Unbeknownst to you he is thinking about purchasing a new game for his DSI. Have him come back a day later and talk about how much the price of games can vary and how by looking around at different places, he got the game he wanted for only $8.00. Let him tell you in detail his whole process of looking for the best deal. Tell him he did a good job!
Congratulate yourself on having such a money savvy son.