What is a reasonable price for replacing roof on a duplex

[Michael A.]

Purchased a 2500 sq duplex close to Dayton, Ohio. It has a shingle roof. About 3 layers. Roof seems to be in its last days and causing some moisture intrusion. I got quoted by one roofer for $6000 to tear off the shingles and replace. This seems too good to be true. This roofer works for other real estate investors in the area. I got another quote from a roofing company in the area for $12,800. I’d like to get the price down to $9000. 

Does anyone have any suggestions for how to lower the price and still have the roof replaced in an efficient way? I’m a new investor. Thanks.