When I think of expense, I don't even think much about the sets because once you have them the cost is sunk and it probably doesn't take much to modify them.
I believe the larger expense is the special effects - multiple ships, aliens, fire power, explosions, collisions, shape shifting, etc. I would argue some of the effects of these series are on par with a movie budget. Lower Decks being an exception, but Prodiigy uses some type of CGI 3D animation, which I'm sure is costly.