Why have all the trouble with triggers? Why not simply create a really, really expensive building in each of the starting faction's capitals that gives you a set amount of money when you tear it down? Then you could also create a building called "Treasury" that costs, say 50,000 mnai to build and then when you destroy the building you get all of the money back. This however, I am not sure about the latter option as I believe that the percentage of money you get back is hardcoded. Still, isn't the first option viable?