This is long, at least read the bit with the smiley faces and the spoiler at the end.
@Ninja no offense taken and I didn't think you were calling me stupid, nor would I have cared if I thought you had.
What do you think the language will sound like when those 12 year olds grow up? When I was a kid my teachers spent hours drilling into our head that it was "Tenser and I". Now if you say that you sound pompous.
@Tenser. Wrong. What necessities do you mean?
There is nothing wrong with accepting language change. It is natural and inevitable and to fight it is a waste of your energy. Why would languages evolve for the entire time that they have been spoken and then just stop when you were born? Why should you care if language continues to change?
@Fun.
The reason why your teacher said it is supposed to be more fun instead of funner is because fun was originally only a noun and superlatives are only for adjectives and adverbs. But, as language changed, fun also became an adjective.
Language has already changed so much that you had forgotten fun should only be used as a noun and you were only using "more" out of blind faith in half a rule. Language should not be about blind faith in rules.

I just went back and reread the original sentence.
I used cheap and fun both as nouns. That does make my argument weaker, but I still say it is not wrong simply because your teacher said it was.
Officially both should have used "more" instead of "er". However no one seemed to notice that cheaper was as officially incorrect as funner.
Saying "how fun is this" and "this is so fun" and "it wouldn't have been as fun without you" are all using fun as an adjective and are as officially incorrect as saying funner. Do you have a problem with "that is a
fun game"?
If your teach had not drilled you on more fun, would you care? Why?
I recently listened to this 36 lecture course on linguistics.
[ame="http://www.amazon.com/Story-Human-Language-Courses-Literature/dp/1565859472"]Amazon.com: The Story of Human Language: The Great Courses (Literature & English Language; 3 Volumes) (9781565859470): Prof. John McWhorter: Books[/ame]
I recommend it. It was very interesting. I suppose if you are not a nerd like me then you would disagree.
TTC - Story of Human Language - John McWhorter (download torrent) - TPB