Is $800 to add flashing to two chimneys a fair price?

I'm questioning an additional charge from my roofer for flashing work on two chimneys. He claims this wasn't part of the original quote, possibly because he mistook old DIY steel flashing for real flashing during the initial estimate, which was done after a snowfall. The chimneys are decorative and must remain for historical reasons, but they need to be sealed to prevent leaks. I'm also wondering if a 50 lb roll of 12-inch sheathing would be enough material for one chimney. While he seems to be doing fine with the rest of the full reroof, he has mixed reviews, having been sued for warranty issues in the past, though he also came highly recommended by a neighbor.