Costs an arm and a leg.
Hit the books.
You can´t judge a book by its cover.
Sleep on it.
Take it easy.
When pigs fly.
Let the cat out of the bag.
Piece of cake.
Break a leg.
Hit the nail on the head.
To think.
Good luck.
Something will never happen.
To study.
You shouldn´t decide upon something based just on outward appearances.
Something is very expensive.
To disclose a secret that was supposed to be kept.
Something that is precisely right.
Something is very easy.
Relax
