I've helped with the beginnings and renovations of a number of ponds. I've been asked to look at many bids and proposals. Generally several pond builders are asked to look at the site, with general guidance about what is wanted. Each will usually see something different than the others. They will each make suggestions. One or more are then asked for an estimated bid. A good contractor will include a set of 'terms and conditions' and usually a list of equipment they will have on site, along with the hourly rate for that equipment, and an estimated total cost. But, there are so many variables, a fixed cost is probably not going to be given on any complex or risky job -- and many are risky. The terms and conditions will define contingencies, like maybe the need to blast, packing an underground water source, digging and sealing a sand or gravel vein, etc.
