Practically....Oklahoma actually. New construction is much easier, everything is already loaded to the roof, we buy their nails and everything, and they do not have to do any clean-up afterwards. And most of our roofs are 60+ squares, enabling them to make some money.
Check your local codes, some areas allow 3 layers of shingles before tear-off is needed. Make sure the quotes include clean-up, haul-off of old roofing, warranty, leaving some shingles in case something happens, insurance, who buys extras ( nails, flashing,felt paper, vent flashings, valley flashings etc.)