When you use the term ‘An Arm and a Leg’ you mean that something is expensive.
Example of use: “Be careful with that! It cost an arm and a leg.”
The origin of the expression ‘an arm and a leg’ is from 1940's America. The earliest written example comes from a December 1949 edition of The Long Beach Independent: “Food Editor Beulah Karney has more than 10 ideas for the homemaker who wants to say “Merry Christmas” and not have it cost her an arm and a leg.”