You're thought processes are interesting, flawed, but interesting.
This is what you do.
You call in 3-4 roofing contractors. Ones who do this for a living, not,"two guys with a hammer". That would be the, "one person said 20 dollars per square off and 20 on."
You give them all a spec sheet of the job specifics so they are all bidding on the exact same job. You ask them questions while they are there initially and then you ask them questions when you get the estimate.
If you post pictures of the house and roof, tell us where you live, we can help with the spec sheet aspect.
If you want the, " hammer guys", you're on your own.
Ron