to be very expensive
TO COST AN ARM AND A LEG
wishing someone good luck
BREAK A LEG!
to try to persuade someone to believe something that is not true, as a joke
TO PULL SB'S LEG
you only just succeed in doing sth,
BY THE SKIN OF ONE'S TEETH
to suddenly become too frightened to do something you had planned to do, especially something important such as getting married
TO HAVE COLD FEET
to be waiting eagerly to hear about something
BE ALL EARS