If you don’t want to use a hosted provider, you can at least just start using git. Just do git init. Then you can start commiting changes. This way, you at least have a history of changes. Then just back that folder up like normal

Then you would probably enjoy concourse

You can use a few tools.

RSync

Rclone - probably want this one over RSync though.

Tarsnap

Duplicati

Restic

There’s obviously a lot more, but these are some of the more popular ones.

Now you need a way to back it up. Probably the best way is to tar it up first and then dump that file. You can also get something like deadmans snitch to ensure backups don’t break.

As you mentioned, if this is just source code, then the best thing would be to create source control and have it set up that way. Then you automate it and deploy the code when you make updates and have a history of changes.

It sounds like tarsnap is your best bet though. It will be the cheapest.

You can also backup to another storage provider like Google, Dropbox, or even AWS s3. S3 can get costly, but you can archive everything to the glacier tier which is pretty cheap.