It's cheap if you already own the hardware. Even $300 could be 50 months (4 year) of a remote server at the prices suggested by some of the posts in this page.

Furthermore self hosting a backup server at home doesn't protect against burglars and fires. You'll probably lose both your data and their backup.

That's why I prefer a local backup plus a remote one (a combination of git repositories and file storage. )

The golden rule of backups;

3 backups 2 local 1 remote

I recently set up Nginx on a DO droplet as a reverse proxy to my home server over Wireguard. It's not $0 but it doesn't directly expose my home IP. And I have an authoritative resolver on the LAN so local clients go directly to the private address.

I would also really like to know how you set this up.

I've been thinking about this kind of setup for my and my family's data, at least.

Can you share how you did this? I’ve had this idea for awhile but never figured out how to pull it off.