Costs an arm and a leg
It means it is too expensive. You can also say “it cost me a fortune”.
Imagine that you have bought the latest version of a computer. Let’s say an ordinary computer costs 4,000 TL, but yours was 10,000 TL. When one of your friends sees it, s/he takes the computer to check it out. But all of a sudden, it slips away from his/her hands and falls on the ground. In panic, you just say: “Oh, no! What have you done? It cost an arm and a leg! What will I do now?” (Let’s congratulate this brilliant friend of us:))