A restoration team might have better use of the money than a CGI team, talented though they are. Peter Jackson's Orc Army I sure cold have funded a large part of a roof, for instance, and that provides your USP, or unique selling point-"Shot on location". Considering the restrictions that would have faced the crew from the 71 film, our production could be filmed in situ.
Oh and another casting came to me, Dame Maggie Smith for GDss Maria Pavlovna, though she'd steal the picture as usual. Ioann Gruffydd's for Felix (see him as Lancelot in the new King Arthur) Ella would have to be Miranda Richardson, beautiful and talented.
One last point, it would be nice to portray N&A rather than major figures of historical import, but with more of a "soap" feel. Humanizing the family in a way the 71 didn't.