To cost an arm and a leg

The other day I saw an advert which reminded me of this idiom. Here, let me show you a picture taken from the insurance webpage:

Isn't it cute?

So, I assume you have already guessed its meaning. However, in case you are still not sure enough, let me show you another picture taken from a comic strip:

And now the final picture with the answer (and some extra examples), so you can check your guesses!

Do you find it useful?

In which everyday conversations would you use it?