It's expensive! Okay, but you should remember the differences about these two examples you give. I mean, I think you know it...Perhaps if you could compare another war3 related map/campaign (uh...DotA?), it would make more sense.
460$ - Assassins creed 4 + Playstation 4
...
And, yes, I agree that a not-exactly complete campaign with a dead forum isn't appealing at all. Also, those prices are scary as hell in every way you see them .
But, even it's not normal, I know some reasons that could "excuse" (not explain, there's no explanation...well, greedy perhaps...) the prices.
1. Despair
.
2. Lack of donators (consumers), that contribute to the raise of ANY kind of price.
3. Inexperience
.
4. A few minor excuses such as "not a must for the campaign" just "extras" or something like that. It's like giving free food, a very good, but spicy food and then sell water for $10 a cup or something...There would be the people who would die from spiciness overdose rather than buying the water, but others would buy it.