Mark:
It sounds to me like a floating dock is what you want. I don't think the cost should be any higher. The corner "posts" are needed only to keep the dock from floating away. As mentioned, Menards has some auger type, galvanized post assemblies you could use. I just drove ten foot sections of 1 1/2 inch galvanized pipe at each of the four corners of the dock. I purchased 2 inch diameter round metal "rings" from the hardware store which are intended, I think, to tie up a horse to. I threaded the pipe through two of these stacked about 6 inches apart at each corner of the dock. This allows the dock to raise or lower with the water level. For good measure, I grease the pipes near the rings every now and then. You can just drive the pipe into the bottom of the pond using a post driver. Unless your pond is of a size that you have tremendous wave action, they should stay put.
