The cost comparison doesn't feel perfectly genuine, because it considers development _and scanning_ of 8mm has to be done in a laboratory while it can be done at home for 35mm.
Regarding scanning, the author spent an inordinate amount of time building this amazing device than can scan as well as shoot; but he obviously could have built instead a machine to scan 8mm film. Even without it, it's fairly easy to transform 8mm film into digital at home; there are many tools to do this.
Regarding film development, I'm not familiar with 8mm specific requirements, but if the author is able to develop color 35mm film, which is not that easy in my experience, he should be more than able to develop at least B&W 8mm film?
Not to belittle this incredible project though!