During the award season of Inception, I remember Danny Boyle saying that Nolan can make a 160M movie look like a 320M one.
Also to give perspective, the new Power Rangers movie cost the same as Dunkirk, King Arthur 175M, and the Mummy 125M.
I think Nolan's efficiency is also because he doesn't use a second unit. He said that it's cheaper to have one unit and a longer shoot than the opposite.
He also trim the script before shooting which means less waste of time and money and also the reason why he's able to present a rough cut pretty early during post.
Dunkirk's VFX shots were finished in 8K, Interstellar's 5.6K, I don't know about the films before that?
Anyway, I know it's not all about the resolution they're rendered in but it does help. I love that with Dunkirk they've finally reached the point where practical and CG are indistinguishable.