Is $12,000 to replace my roof a fair price?

I'm in the GTA in Ontario and I'm getting a new roof put in a few days. I shopped around and went with a company that has a physical location, is established, and has good reviews. They charged me $12,000 for my roof, which was one of the best prices I got after speaking with 8 different roofing companies. My friend has a similarly sized house (about 2400 sqft) and found a company online to do his roof for $6,500. These guys are known for giving 'honest' pricing. I can't tell if I'm getting overcharged or if he's getting scammed, as I feel his pricing is incredibly low. My house is slightly larger at 2800 sqft, and both our roofs are pretty simple. I didn't go with the lowest bid; I chose an established company with a physical location and good reviews, and I even visited previous customers. They actually beat most of the smaller companies on price.