$6/hr.? LOL! Good one!
In all seriousness, I charge $100/hr. with a one-hour minimum. For that price, I'll come out and take a look around, go back to the office, write up a report and protection plan, and send a copy to the client and our city arborist. Keep in mind I'm talking about a job site where a residential builder/developer is putting up a house or duplex and wants to stay in the city's good graces. What you're describing sounds like a pretty involved survey. With that type of a gig, you should let the client know that you'll come out and view the site, noting the number of trees, and then give him/her a written estimate of how many hours your detailed pre-construction survey and report will take. You should still charge your $100 for the hour it will take you to check out the site, and send a written report of what your final report will contain, following whatever is required by the local governing body/code. I have found that "free estimates" in commercial work usually gets your brain picked by the developer who then hires his brother-in-law from out of town to come in and follow the plan you've run down to the developer while you're on the site for your first, and last, visit. I literally had that happen to me last month. Funny thing is, the developer absolutely ignored my plan that I gave him, for free (thinking I would be doing the work) on-site, and then called me after he had put up the house and run afoul of our city arborist. Yesterday I went out there, made my notes, collected my $100 and then sent him my detailed remediation plan which I also sent along to our city arborist. He's looking at my bid of $4000 now, but I have a feeling he'll call his brother-in-law again. At least I made a fairly easy $100, this time. Oh yeah, do get the book on trees and development by Matheny and Clark. It is loaded with great information.