cost an arm and the leg
to very expensive
under the weather
if someone is under the weather they feel ill
when pigs fly
something that will never happen
break a leg
you say that for good luck
hit the sack
go to bed
call it a day
to decide that you have finished doing something
see eye to eye
if two people see eye to eye they agree with each other
the last straw
problems that makes impossible to accept
spill the beans
to tell people secret information