Most of the money seems to have gone on the giant warehouse, er I mean Tardis set, which frankly I'm not hugely fond of anyway, I mean it's better than Whittaker's, a lot better, but that's the only modern Tardis set I prefer it to.
Wasn't the Whittaker era supposed to be better funded, or using much better camera technology. It certainly seemed more expansive, but then oddly that was just another thing that seemed to have a counter effect, the screen looked very empty at times.
The production team can be clever as well, reuse sets the way they had the Satellite 5 sets used in 3/13 episodes in Series 1. Piggyback on the production of a period drama so you can share costs for one episode etc.
Hell here's a radical idea as well, why not go back to 25/30 minute episodes? (I'm unsure if this would actually save money but logically it should) there are plenty of shows that prove you can pack a lot of plot into that time frame if you're writing is good enough (take Lower Decks, Skeleton Crew, many sitcoms etc, plus of course the SJA!)
Again what would you rather have?
No Who
6 x 45/60 minute episodes
10/12 x 25/30 minute episodes