How dare you make fun of Yum Cha!!!!
The way to tell how much you have to pay is where the stamps are on the slip. There's ontl three or four areas the lady can put the stamp, and thats on 'small', 'medium', 'large', and maybe 'X Large'. These are the sizes of the dish you choose. Obviously, small is cheaper than large.
If you have more stamps on the large, then well, expect a hefty bill

Some restaurants have the price of the small, medium, etc dishes, so you could basically work it out from there.
Yum Cha is yum!
And in the US, they call it Dim Sum for some reason, but I guess they both mean the same thing.