1. That's great! 很好！

Fantastic!/I'm glad to hear that.

2. How much are you selling it for? 这台的价格是多少？问价钱的说法还有：

What's the price for it?
How much does it cost?

3. You can't go down on the price. 意思是问可以再价钱可以再少一点吗？讨价还价的说法还有：

Could you lower the price some?
I would buy it if the price was lowered.

4. By how much? 一般售货员问还价的买主，意思是价钱降到多少合适？

How much are you talking?
How much lower?