Bargain vs moderate

[Monica]

Hello. In the following multiple-choice exercise:
"Here is a wonderful opportunity at a .............. cost to visit the truly remarkable island of Cuba."
A cheap B moderate C bargain D small
The answer-key gives B moderate as the only possible answer. However, I had done a search in google and found quite a few instances of "bargain cost", so why is this incorrect? As usual, thank you for your help.

[Jamie (K)]

Monica, notice that in the Google results, the words "bargain" and "cost" are usually not part of the same collocation. You find things like:

Will Noun Phrase[that bargain] Verb Phrase[cost you more than expected?]

It's common to say "bargain price", but it's unusual to say "bargain cost".

[Molly]

Where you happy with the answer you got here?

http://forum.wordreference.com/showthread.php?t=984664

[Monica]

Yeah, I had the feeling it was only a matter of collocations, I just wanted to make sure. Thank you.