Good idea about making the cost high. I think by balancing what you want them to build easy and hard it can be done.
If you removed the basic shipyard, resource extractors, research, and intel from the pirates and created high cost/lower valued alternatives then their expansion would be naturally slow and of reduced value.
Pirate research facilities should generate ~250 points. Most of their research gains should come from capture so the amount of research they really need is not nearly as great as a standard empire. If pirates could get to ~20,000 research later in the game that would seem to be enough.
With low maintenance and scraping facilities their resource needs are low. They should get a large percentage of resouces from scrapping captured ships.
Intel has been worked on.
this leaves shipyards. Creating a pirate shipyard that builds at say 1000 each would be a reasonable start. No addition shipyard facilities should be availble. Shipboard one definately.
I can't think of any other area that needs to be controlled. They should be able to research all the other areas but it will be a slow process. With the built in penalties in the pirate culture there will be many more reasons to capture ships for scrap value as opposed to building an empire of colonies, which is what Pirating was all about
