That is a slightly tough one. But here's a few numbers I come up wth.
10,000' long x 10' wide= 100,000 sp ft. divided by 43,560 sp ft acre = 2.3 acres
Not knowing how experienced an operator you are let's go conservative. A good skid steer operator does not automatically equal a good mulcher operator, a good start but still a big learning curve.
Usually it takes about 5 hours per acre. Given the newby factor that goes to 6. Then add the material size that would go to 7, then add limited area to manuver and that can easily go to 8 hours per acre. Plus you will have to stop for lunch in there, fuel the tractor and blow out the radiator.
Now if you were charging by the hour it should be near 150.00 per hour. An 8 running hour day should be 1200.00 or by the acre 1000.00 per acre. If you can go faster better for you. If you can get either of those your still good.
That would leave you at 2 days if things go well, 3 days if slow. Have you walked the whole fence line yet?
Now I know you asked profit numbers but you can figure from what I put above and see where you are. I can imagine the rental isn't cheap and I'm surprised you found one for rent. Too bad you can't sub it out beacuse that would be the best for you and a mulcher. A contractor with a large machine could knock that out.
One idea is Oh, that guy running the mulcher works for me. They really can't expect you to literally do ALL the work. See what you think about that.