The price of shingle can vary, depending on your part of the country. Furthermore, roofing shingles are petroleum based product, so when the price of oil goes up, you can expect the price of roofing shingle to do the same.
In the Northeast a <a href="http://www.mbmcarpentry.com/services/roofs">Chelmsford roofing contractor</a> will charge anywhere between 375-450 per square ( 100 square feet ) of roof coverage. This price would include doing a full tear-off of one-layer of roofing. It would also depend on what level of roofing materials you wanted to use.