One of the frustrating things about pond building is there is no template, or model to pattern. Each site is different. I have seen an eight acre lake cost $6,000 and a six acre one cost $32,000. But, there is a template to get an idea of what it should cost, for your site. The more planning you do, the more accurate cost projections will be.
The world is full of honest earthmovers, making a fair living. As expert as they are, it's incumbent on the landowner to guide the contractor, not vice-versa. In order to do that, the landowner must know as much as possible about the project, before any dirt is moved.
With dense trees and brush with harsh slopes, it should cost as much as $1,000-1,500 per acre for clearing, tops. Normally, clearing runs $150-400 per acre.
Brettski, you mentioned it wasn't possible to get an estimate. I certainly appreciate the degree of difficulty for your project, but today's advanced technology allows us to make projections which weren't available several years ago. Even as inaccurate as gps can be, you should be able to get an approximation of the amount of clearing to be done, beforehand. Also, designers and engineers can accurately calculate the length, width and height your dam should be. That creates an idea how much dirt needs to be moved above the ground. With some test holes, designers can give you an idea how big a core trench needs to be, and how much dirt should be moved below ground.
Then, using gps or a laser transit, flag the shoreline, to determine the configuration of the lake. At that time, you can see how much shallow water you will have, what the bottom will look like, and how much work needs to be done to provide habitat.
You didn't mention your goals, so it's tough to guide you beyond these tips.
The hourly rate for the equipment is fair. It sounds like you have reputable people working for you.
What's missing, to me, is a projected plan. You guys are building a lake by the day, by the hour, making decisions on the fly, because it seems, you think that's the best way for this site.
If I am you, the next thing I do is get the NRCS out there, or an engineer, to stake the dam site. Have the excavator dig a few test holes to look at soils below the ground. The kind of dirt you have helps dictate how (and how much) to build the dam. Once you know dam size, your designer can project costs.
Last, but not least, keep in mind several things. You are not only building a dam, you are building a lake. A dam is a water management structure, a lake is a habitat teeming with life. It's your job to make sure the habitat matches your goals. Decisions you are making now will impact that environment for a minimum of four generations beyond you. And, two or three years from now, when you are in a boat, enjoying the serenity, you don't want to look around and say to yourself, "I wish I had done it differently."
