Interesting thread. The price for tying in new shingles will include replacing 3 courses of slate. Not only that, any additional slate will cost $25.00 each to replace.
Those are Vermonts and at the end of their life. AND, the roof area is nearly flat and unsuitable for slate or shingles.
Not to mention, the roof is 6 years older than it was when that photo was taken.
Since I can't see the whole thing, I'm guessing the cost at $3,200. per side.