I don't know. Can you give us some tips? This is a very unusual expression.

Actually, you would never say that. It is grammatically correct, but I can't think of a reasonable situation where you would say it. You are saying the the person is very expensive! Perhaps you mean: "You must have spent a fortune!" (When somebody has spent a lot of money) or "That must have cost a fortune!" (When something is very expensive)

Sorry, I got this wrong. I thought you were talking about normal conversation. "Two and a half Men" uses absurd and outrageous humor (quite effectively, I might add.) If I'd known where it came from, I wouldn't have ruled it out. I was thinking of a situation where you might refer to a person in this context. Consider a rich old man who has a very young girlfriend for whom he must buy expensive presents to keep. "She must have cost a fortune." could actually be used. One point - if the girlfriend made the statement, she could have been talking to the diamonds. I'd have to see the episode.

She said: THEY must have cost you a fortune. Listen again.

I think I saw that episode. Was it when Charlie said to a girl that he thought had nice boobs, "you must've [must have] cost a fortune"? I think he meant that her boob job cost a lot of money, therefore it looks like (is obvious) that she was had a lot of work done on her to make her look that good. It is a sarcastic remark made to mock that person (make a joke of). Not usually a good thing to make fun of a person (make a joke about someone's appearance).