Yeah I do scale modeling for military vehicles and a good kit is like $30-50 bucks max. Though I don't go above 1:48 and do mostly 1:72. That scale would put a modern jet at about the size of a 40k flyer like a heldrake. Some of the kits are just as intricately detailed, especially newer zvezda kits.

GW justifies it by imagining that they don't have competition from other game+model systems. Historically that's been true. But it's slowly becoming not true. You're partly paying money for the upkeep necessary for the game system. In a display model, once the mold is made and the product is on shelves it's hands off. No more money or time needs to be put into it.