As you know Tosh, area does come into pricing. (maybe that is another topic)
You go into a Garage, not a main dealer, just a repair shop etc. You say, "My car needs a service, it might need oil change, oil filter, spark plugs, air filter, brake pads, oh, and can you sort out a smell of fuel! I think it's got a leak somewhere."
"How much will that be?" They can't tell you. "OK", you say, "What do you charge per hour?"
Some, most will tell you their labour charges per hour. Lets say it's £30 ph. and they take 3 hours, and they sort your problems. You get a bill for £227.41 + vat.
You are horrified! They only said £30 ph.
They are no different to us. They see what type of vehicle is rolling in, the rust, the neglect etc, you, your status..They see it in a thrice!
In short, we do the same..use all your resources, walk around the house, get a figure in your own mind....Keep to the one you would like
If you can do the job before you quote, remember, they just want the windows cleaned! Time it! Bingo!
Don't make the mistake of telling them it'll be cheaper next time! How you price it first time is how it is.
Pj