Yea, you're quite right with this, but It's obvious it will be more expensive to print out 1200+ pages compared to original estimate of 700 or so.
So as someone said, he's only human and he couldn't predict this historical subject would have so much more to tell us about. I'm sure Bagnall will deliver most entertaining history reading of all. Even if we have to "contribute" a little extra waiting time and money.
I think cutting out lots of material would make for incomplete reading and it certainly will be worth waiting in retrospect.