I finally took the plunge and deleted the time-wasting cesspool that is facebook. I've been considering it for a while, but kept it around for whatever reason. I did download all of my data, which ended up being a ~270MB zip file. If that were the average amount of data on each active user, that's 602 petabytes of data. A petabye is a million gigabytes. Going off of google's storage pricing (https://cloud.google.com/storage/archival/) that would be $4.2 million per month just in storage fees. I'm guessing I'd have far less data than the average user as I haven't post much over the last several years, so that number could be way higher. That's an f-ton of data.
All that aside, if you've ever considered getting rid of facebook, I'd definitely recommend it.