Is $13000 a fair price to replace a 2500 sq ft roof ?

We have to get our roof replaced due to the previous seller (a guy who flips houses) just throwing the new shingles over the old (without even nailing the 2nd set down!), and we got an estimate of $13000. Now our roof is approx. 2500 sq ft and they are installing gutters too. My wife & I would like to know if that is a fair price. The contracting company is through Keystone Help, a program for Pennsylvanians fixing their homes & they are required to guarentee their labor for the length of the warranty on the shingles (so 25 years in this case). They also don't get paid until a Keystone Help inspector approves the work. We just want to make sure it's not too high because that is alot of money. Thank you for any input.