It really makes a difference on the type of work you need done. I think you need to get more than 2 estimates. Its hard to predict the price since they aren't going to know the condition of your roof until they start tearing off the shingles. You could find yourself with rotted wood which will add to the cost. I found a really good site on
HOW TO GET A GREAT ESTIMATE.
Owens Corning has a list of preferred Contractors on their site.
See HereALLEN AND SONS
Preferred Contractor Asphalt Roofing
1909 SHAW ROAD
DURHAM, NC 27704
ALUMINUM CO. OF N.C.
Preferred Contractor Asphalt Roofing
1335 HAMLIN ROAD
DURHAM, NC 27704
PICKARD ROOFING COMPANY, INC.
Preferred Contractor Asphalt Roofing
823 E. TRINITY AVENUE
DURHAM, NC 27704
RESIDENTIAL ROOFING & REMODELING
Preferred Contractor Asphalt Roofing
1408 CHRISTIAN AVENUE, SUITE 34
DURHAM, NC 27705
Most sites quote to strip and reshingle on medium sloped roof around $2.50-$3.50 per sq.ft. It looks like you are getting a deal. The price they quoted you seems very low.
You should really think about your reason for replacing the roof since you are just going to move anyway. If you feel that you absolutely have to replace the roof then don't go top of the line. If you can't recoup your cost of the roof then it will be a waste of time, effort and money.