We did the bid process here. We have a rule of thumb about 3 bidders for any job over 5K. We did not choose the cheapest, but the guy who came recommended by others. The most expensive bid was also by far the most knowledgeable about pond building, and in some ways I wish we went with him, but we did not. It is too late now, the hole is dug. The pond turned out fine, but isn't really what we wanted. Smaller, and just a bowl, pretty as it is.
The problem with pond building, it really isn't live an learn. You make a mistake and you pay... It really needs to be done right the first time, or you pay in anxiety, sleepless nights, and money.
I would spend the extra money if you are doing a project that large and get EXACTLY what you want. A leak-free anxiety-free body of water.
