Welcome to English in a Minute.
Let's say you buy something. And when you pay for it, you say: This cost me an arm and a leg!
Do you have to give them your arm and your leg? I hope not. Let's listen to an American English conversation to see if we can find out what this means.
A: Did you buy that new computer?
B: Yeah, I did. And it cost way more than I expected it to.
A: How much?
B: Let me just tell you it cost an arm and a leg!
When you say in American English that something costs an arm and a leg, it means that the price is very, very high.
If you use this phrase, everyone in the United State will understand you. But this is an informal phrase, so don't use it in a business setting.
And that's English in a Minute.