Hello, a good rule of thumb for new work is that will get you real close to the competition is 3 times the materials costs.
So that if the total materials for the 185 feet, add up to $10,000 you would bid $30,000... and that would be for a common job, with the board walk just a few feet off the ground.
.. then you have to decide how long it will take you to tear down and haul off the old board walk and how much money you want to make per hour. Most companies will bid that work at $50 to $75 per man hour, plus trucking and disposal costs at the land fill... that would be the minimum.
After you get that figured in, add 10% or 15% to cover your risks and any costs that you might have forgotten to include. To pay for the job, collect 10% in advance, and then more money when you have the old board walk torn out.
Then when the lumber is delivered for the new board walk have the customer pay for that. That way you will not run out of money, and the only risk will be your labor.
Good luck with the project.
We are on the honor system here. Please remember to rate my service before you leave today. It is how I earn a living, and does not increase your charges.
If you need anything else, just let me know. You can continue asking follow-up questions at no additional cost.