If you already speak Korean, you won't have a problem asking 'how much is that?' in Korean, which is "얼마예요?" but a lot of people are thrown back by the responses and extra questions that they get from the store clerks because they didn't expect those complicated questions that they never studied or heard before in a book or in a tv drama. So here's a few expressions that you can expect to hear in a cafe or in a store in Korea after you pay for your drink or what you bought.
Here's the link to the video I made a few days ago:
http://www.youtube.com/watch?v=yDhM-PUM-5A
Thanks for watching!