I have been discussing with some friends in the UK about the prices of aircraft in the marketplace. The main issue is:
Xbox players can only buy from the marketplace. So now, the question is, who sets the prices for those aircraft, and could MS say no to adding the plane to the marketplace if they think the price is too high?
The price is set between the addon creator and MSStore.
Naturally, MS has the last say, it is after all their site.
They can do as they wish.
They do have strict criteria that must be met before items are accepted to the Store.
However, I very much doubt they would ban something due to its cost.
If people want it, and it meets the criteria, it will probably end up there.