The book that I bought yesterday is good but expensive.
我 昨天 买 的 书 很 好 可是 很 贵。
This is more expensive than that.
这个 比 那个 贵。
This is 20kuai more expensive than that.
这个 比 那个 贵 20 块。
Is the fruits in China expensive?
在 中国 水果 贵 不 贵？
This really isn't cheap.
这个 真 不 便宜。
Going by plane is faster but more expensive.
坐 飞机 快 可是 贵。