Pricing is a TOUGH one. Only you know what it costs to run your business.
I do a LOT of Construction Progress Documenting (I'm in the construction business already). My area supports a higher price than some for this type of service but (this is going to come off bad) I bring a lot of experience and knowledge to the table. I visit construction sites often, know construction inside and out, and I have both Commercial and Residential Construction knowledge to be able to add value for my clients. I can notate details, document assemblies, and in one case even noted a drainage issue that was not noted except from me.
We charge $250/trip unless they book in BULK and that price goes down "some" depending on how many site visits they want shot.
You need to figure out how much preplanning is needed (some site visits may be needed prior to flying), how long you'll spend traveling to the site, how long ON site, how long in Post Processing, how much you'll have invested TOTAL per shoot, and then how much you NEED to make per hour.
You really need to take the time to get a solid and comprehensive Business Plan put together. This will not only help you establish your price structure, it COULD save you some $$. I teach my students to always START with the BP before they spend a single penny on equipment etc. You need to know where you ARE before you start down the road of running a small business.
Also the Business Plan will, through the building of it, teach you what your competition is charging and maybe help you know better what your local economy will support. If you come out charging too MUCH or too LITTLE you may be setting up for failure.