Their donate page says they host 45 PB of data (45k GB). That is a mind boggling amount of data to have available online and can't be cheap. This is absolutely a cause worth donating to.
I found this picture where they'd just bought a few hundred brand new 4 TB drives: https://commons.m.wikimedia.org/wiki/File:Incoming_additiona...
Sadly there's not really a great one-stop page for this kind of info -- https://archive.org/web/petabox.php exists but is sadly outdated (I'll see about rewriting it sometime). We do public tours on Friday afternoons of the main office/datacenter (and our big annual event is coming up next Wednesday if you happen to be in the Bay Area: https://www.eventbrite.com/e/world-night-market-the-internet... )