money doesn't grow on trees

said to warn someone to be careful how much money they spend, because there is only a limited amount

(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

"Mum, I'd like a new bike."

“妈妈，我想要辆新自行车。

"I'll have to think about it - money doesn't grow on trees, you know!" ”

“我得想想看──你知道，钱可不是从天上掉下来的!”