The star wars licence can't be cheap, they have to have stuff made assembled painted then shipped from China so that's a significant up front cost.
Plus they don't know every ship will sell, look at tie advanced they've never been hard to find.
So while yes they could sell for less they probably don't make as much per model as gw who sell 50p`s worth of plastic for £50.
None of the ships are hard to find. They're mass produced, and importing from China is easy, especially thanks to Clinton.