well, i did a similar job for a trophy managed hunting club that is on a beef cattle farm. I can tell you that I did not have near enough traps to even start to think about trapping 1500 acres -- when you are on a limited time frame and charging, the more steel you got in the ground the better your chances. There is no way to eradicate them around here and they know that, they are just trying to keep the population managed.
I did not have enough traps when I started the job -- but will have more when I return. I gave them a fixed rate per week for 4 weeks of trapping. Things to factor in -- trap check time -- every 24 hrs, 48 hrs, etc., bait, lure, gas to and from, insurance costs, trap wear and tear/replacement, etc. Like Kirk said, charging by the yote will proballly not be a good idea.
If folks are paying, they expect results -- YOTES -- quickly. If this is something new to you, maybe talk to the landowner and get your bait, and gas back and forth covered and use it as a learning experience -- some will disagree with this approach, but it has served me well. I get repeat business from some clients and referrals from others even though my price goes up.