This is 20kuai more expensive than that.
这个 比 那个 贵 20 块。
Was the cellphone that you’ve bought expensive?
你 买 的 手机 贵 不 贵？
Their dishes are both good and cheap.
他们 的 菜 又 好吃 又 便宜。
The more people are there, the more expensive the stuff is.
人 越 多 东西 越 贵。
The book that I bought yesterday is good but expensive.
我 昨天 买 的 书 很 好 可是 很 贵。
That is expensive, this is slightly cheaper.
那个 很 贵，这个 便宜 一点。