This past summer, my 12 year old accomplished several of the big tasks for my parents. They paid him $50 and gave him a brand new, crisp $50 bill. He still has it and is determined to keep it for a very long time. There have been two instances where he has thought about buying a toy or game but has opted to save his money because he does not want to part his cash!
The desire to hang on to that $50 bill has caused him to analyze and critique his spending habits. He really thinks about whether an item is "worth it or not".