I want to buy watermelon.

When you are in a groceries shop and try to buy something, this is how to say it in korean language.

A: 수박을 사고싶어요. I want to buy watermelon.
B: 수박 사러 가자. Lets go to buy watermelon.

A: 이 수박 얼마예요? How much is this watermelon?
B: 만 오천원이에요 Its 15,000 won.

A: 너무 비싸요.. Too expensive..
B: 이것은 만원이에요. This one is 10,000 won.

A: 두 개 주세요. Give me two please.
B: 여기 잇어요. Here you are.