Just located a place that does all-rope moorings, for substantially less. The rope has a breaking strength of 19,000 lbs. (apparently they now use 25,000 lb. rope), and it's floating rope, that is semi-weighted to keep it off the seabed.

So, it's substantially cheaper than chain, and won't/shouldn't chafe on the seabed since it is not supposed to/won't lie on the seabed.

Also, evidently I could get two blocks put in; the second block would only be an additional $500, as a back up to the first block, so that it wouldn't drag in a storm. Apparently, yearly maintenance would involve going down the rope 20-30 feet and scrubbing off growth (below that there's not much oxygen or light for growth). You'd obviously also have a diver check the attachment point to the concrete blocks yearly or every two years.

Anyone else have any experience with rope moorings? The system I'm contemplating having installed is this: http://www.mooring-buoys.com/product.html