否定是inexpensive，中文意思是adj. 便宜的
She found a small， inexpensive motel on the outskirts of the town it was barren and unlovely.她在镇郊找了一个又小又便宜的汽车旅馆，设施不全也不好看。
Import fees are low， so tourists enjoy inexpensive shopping.
进口费用低，所以游客可以享受便宜的购物。
expensive是形容词，否定的用法可以考虑这几种种情况：
1、反义词cheap，便宜的
2、加前缀un，unexpensive，不贵的
3、借助be动词，如：It isn’t expensive.
