There are really 3 factors at play here...
1) How high your roof is
2) The type of equipment being installed
3) Labor required to install it
The antenna equipment probably costs the guy anywhere from $175-$250, the real issue for him is getting on your roof to install it.
This is not like installing a Dish where you can get away mounting it near the gutter. The problem is the guy actually has to climb to the peak of your roof.
Take my house for example, it requires a 32 foot ladder just to get above the gutter, and then the roof is so dam steep I would then need a secondary chicken ladder just to make it to the peak.
The wiring in my house is a breeze, since when the roofers put my roof on I ran a RG6 and a Rotor wire through the roof vent, but the problem for me is getting up there!.
Im too scared to go up there and none of my installers will go up there! I had to settle for a square shooter antenna in the attic instead!
I have literally considered renting a cherry picker to get up there to install a real ota antenna