^You're not comparing like with like. SG & Friends had definitive casts who the audience wanted to see together. By its very nature, DW rotates and changes cast, from lead onwards. There is no need to worry about the incumbent actor wanting a pay rise when there's a built-in in-universe explanation for replacing him.
As regards the budget thing, a DW film is still going to have to be funded by the BBC, which has a finite budget. Should they spend the equivalent of an entire season's budget on a 2 hour film just so that we can see cooler SFX on the big screen?
As regards the budget thing, a DW film is still going to have to be funded by the BBC, which has a finite budget. Should they spend the equivalent of an entire season's budget on a 2 hour film just so that we can see cooler SFX on the big screen?