This is the wrong approach. You don't need to add anything up. You can take a dynamic approach. Just estimate the
current cost of developing the next n meters of space around us, then estimate the growth curve that maximizes liquidating as many resources as possible, and then do an integral to calculate the amount of money we could conceivably develop before the universe turned to grey goo.
Ironically, I think undertaking the project would actually hasten the advent of grey goo, shortening the life of the universe.