http://dvice.com/archives/2012/02/it-would-cost-8.php
Ok the above link will tell you the cost of building the death star. Now obviously with today’s tech it would not be possible to build something the same of a small moon anyway but hey...
Ok so let’s assume you were going to build a ship the size of a small moon. First you would not be buy raw materials, no you would not. You would take you small fleet of robot ships and part them next to a nice iron rich asteroid belt. Allow them to start harvesting iron from the rock, forming really large sheets of the stuff, and finally building a hull. I am not sure if pulling solar power would be enough or you would need to go nuclear but either way other then setting up the power plants you would have to have limitless power. As you finished the hull the power plant could then become the power supply for that. After the hull was finished the robot fleet would have to continue to pull the raw material from the sounding rock as the interior started to take shape. In concept you most likely could pull enough water in the form of ice from the asteroid belt but you might have to bring some of the along which would mostly likely mean purchasing it, getting it from a non-owned plant unless you want to concur it. Mind you I guess the owned their part of space anyway so taking what they wanted may not be too much of a problem. Anyways as the inside started to form more and more personally could be moved in and manufacturing setup to build whatever equipment you need inside.
So overall I think besides the initial investment and maybe playing the help as they move in, assuming you pay them (evil emperor and all) I don’t see where the cost is that high. But what do I know?
first test
second test
third test