For that kind of money and perhaps even 50% less you should be able to build a 4kw aux electric drive with regenerative ability. You could possibly turn that system into a drive as in theory any generator can be turned into a motor by supplying power to it.
Also, how often are you actually moving at 3 knots or more compared to just hanging out in an anchorage or whatever? I guess this works well for those areas that have a good current as well.
See your points. The price has to come down, and it is a device most suitable for the long distance sailors. Those who sail along the coast, hopping from one harbor to an anchorage will get shore power and/or extra juice from solar panels at a much lower cost.
All the best, Jon www.thesailblog.com