Cost/pay an arm and a leg
Definition 1 of 1
Pro Tip 1/3Exaggeration
The phrase is an exaggeration and not to be taken literally; it indicates something is very expensive. 
That designer watch must have cost you an arm and a leg!
Pro Tip 2/3Informal Tone
Used in casual conversations, not in formal writing or speeches. 
I’d love to go on that trip, but the tickets cost an arm and a leg.
Pro Tip 3/3Humorous Context
Often used humorously to comment on the high price of something. 
Eating out at that fancy restaurant would cost us an arm and a leg, we'd be broke!