give (one's) right arm
A figurative phrase that highlights one's interest in having something or eagerness to do something. A: "I'm going to the concert on Saturday!" B: "Aw man, I would give my right arm to have tickets to that!" I would give my right arm for your sister's gorgeous hair!
would ˌgive your right ˈarm for something/to do something
(informal) want something very much: I’d give my right arm to own a horse like that.