I used to do this to save the $6 and backup locally. Unfortunately, it stopped being practical once the backups hit 3-4 GB since they'd interfere with my internet access in the morning.
Realistically, what I'd do, is have each founder [or just any 2 technical folk really] each setup seperate accounts at two vendors [e.g. Backupsy + Kimsufi] and have the VM pull the backup from the source. I'd keep a week's worth of backups in this way.
No one person could destroy 100% of the backups. A single breach would not destroy 100% of the backups [although it might destroy the production environment depending on permissions].
The cost for such a solution to cover like 1TB of data? $40/month x2.
If you are a funded startup and you aren't able to spend $100/month on securing your backups I'm not sure what to tell you.
3-4 GB of data each day?
I backup data from my personal laptop to digitalocean droplet ($5 month) and then during the night backup droplet (which also stores my mail and other stuff) to the disc connected to raspi in my home. Incremental backup (rdiff-backup) takes literally 5 minutes (3 mins for /home and 2 mins for mail). And amount of data slowly approaches 9GB.
Full backups are less efficient, but significantly safer.
It is just a snapshot of the entire database.
It's not hard - you just need to do it.
Why not to a big disk sitting on a computer in your house?
The server doesn't push to it, the home computer pulls from the server (via a cron job or something). That way an attacked can come in from somewhere else. It doesn't have to be perfect, and it shouldn't be your only backup. But having something like that is great for catastrophes like this.