Conversation A

What would you like to buy?

I would like to have that one.

That is 300 RMB.

It's too expensive.

Conversation B

How much is that?

100 RMB.

It's too expensive. Do you have anything cheaper?

How many do you want to buy? It's cheaper (if) you buy more and it's more expensive (if) you buy less.

I would like to have three pieces. How much is that?

200 RMB.