That's unreasonable! I'd take it for (100 yuan) 
这真是卖得太贵了！如果（一百块）我就买。

How about (100 yuan)? 
卖（一百块钱）如何？

I'd buy this if it were cheaper. 
再便宜一点我就买。

Lower the price, and I'll consider it. 
价钱低一点我才会考虑。

It's a little overpriced. 
这标价有点贵。

I like everything about it except the price. 
这东西除了价钱之外我都喜欢。

I've seen this cheaper (in) other places. 
我在别家有看过更便宜的。

I heard other stores were having great mark-downs on this item. 
听说别家的这个东西在大减价。

If I buy more than one, will you give me a discount? 
多买一点有折扣吗？