King Reza: I'd not say inexpensive is the synonym of cheap. Even saying it's low priced is a better opposite. Something cheaply priced maybe, but to just say cheap is not how I'd say it.

Further research found this link:
http://www.synonym.com/synonym/inexpensive
Perhaps you're right about cheap and inexpensive. It just seems that where I live the word cheap is not used for some reason unless there's something wrong with what it is you're talking about. Perhaps this is just in my area and how advertisers and television can twist the meanings and usages of words.

By the way this link might help you find lots of opposites and alikes (antonyms)