Did a research project on mycelium as a construction building material in my sustainability class. Although I am sure they have brought down the costs, cheap was not a word I would have used to describe the production of these building blocks. That was using sawdust and other waste organics for the mycelium to feed on. I would think the cost to produce algae in sufficient enough quantities would have additional costs unto itself. Would be interested to see the cost analysis for this vs the alternate. For use in space obviously the options available and their costs change dramatically I am sure.