Multiple estimates a good idea. How many courses are on roof now? In Mass. if you have two layers on, you must rip before installing new shingles. =More labor and disposal costs. Is not to say that roofing over single course is bad, but if leaks are in valleys, peak, or edge, you may not resolve the problem. Water and Ice Shield along edges if you rip are worth the money. Drip edge the gable ends too, I see this skipped way too often for my taste. I would like to be putting the composite fake slate roofing on my house this spring, but material cost is outta sight.....

Wait till they START rebuilding New Orleans, then you'll really see prices spike. sorry, just finished three bids and had to vent