这个多少钱?
How much is this?
How much does this cost?
What does this cost?
What is the price of this?
How much? *比较生硬的感觉。 多少钱?
Could you tell me how much it is? (您能告诉我多少钱吗?)

如果你买的话就是说：
I'll take this one. (我要这个。)
All right, ma'am. (好的。)
I'd like this one.
I'd like to buy this one. (我要买这个。)

讲价就说这个
能再便宜一些吗?
Would you give me a discount?
Would you give me a discount? (能再便宜一些吗?)
Can you make it cheaper?