Small lots are a one day job and they are quoted the same way. Text a photograph and the address and you get a number, not a range and not a site visit you have to schedule around.
It is also the cheapest thing you will ever do to the outside of your building, which is worth knowing before you price a sign.
Or put it in writing
For the lot you are looking at right now. Address and rough stall count help, but a name and a number is enough to start.