EXPENSIVE
(TO BE)

guì
CHEAP
便宜
piányì

That is expensive, this is slightly cheaper.
那个 很 贵,这个 便宜 一点。
Nàge hěn guì, zhège piányi yīdiǎn.
Could you give it to me a bit cheaper?
你 能 不能 给 我 便宜?
Nǐ néng bùnéng gěi wǒ piányi?
This really isn't cheap.
这个 真 不 便宜。
<Zhège zhēn bù piányi.>
It is too expensive. I don't want (it).
太 贵 了,我 不 要 了。
Tài guìle, wǒ bù yào le.
This is too expensive.
这个 太 贵 了。
Zhège tài guì le.
This is more expensive than that.
这个 比 那个 贵。
<Zhège bǐ nàge guì.>