money doesn't grow on trees
Money should not be wasted because it is not something that can be replenished whenever one wants. I can't believe you would spend your entire allowance on a silly video game. Money doesn't grow on trees, you know!
Money does not grow on trees.
Prov. It is not easy to get money. (Implies that the person you are addressing spends money too easily.) Child: Can I have ten dollars to go to the movies? Father: Ten dollars?! Money doesn't grow on trees.