money doesn't grow on trees（提醒别人花钱时要谨慎）钱可不是从树上长出来的，钱可不是从天上掉下来的，钱来之不易。

【例句】
My daughter Claire wants a car for her 17th birthday, but I can't afford it. Money doesn't grow on trees!
我女儿克莱尔想要一辆车作为她17岁生日的礼物，但是我买不起。钱来之不易啊！

I can’t give you any more pocket money, Alice. Money doesn’t grow on trees, you know.
我不能再给你更多零花钱了，爱丽丝，钱不是从天上掉下来的。