I believe this could be easily fixed with some type of automation tool? I use Keyboard Maestro and if I’m expected to get 1 file on my Dropbox with a certain name, for example, I can automate that to run daily or whenever I’m supposed to get the file and if nothing is there, it could show a notification.
Would something like this work for you instead of manually checking it?
Wow, that’s a lot! i can see it getting to that on communities with lots of engagement, lots of uploads, and lots of years of activity? So, for now, I guess I will be ok with very small backup files that fit my Dropbox.
And even if I decide to use AWS or BackBlaze, 5-7 dollars a month is good enough to bring some peace of mind. If there’s budget for that, I value my mind more than my wallet 
Really appreciate your time and help on this (and checking your bills and stuff)! 