[buro9]

I just use Tarsnap for this scenario: http://www.tarsnap.com/

What I am looking for is a folder that syncs, but is secure and open source.

BitTorrent Sync is the closest to how it should work, but is not open source: http://labs.bittorrent.com/experiments/sync.html

[StavrosK]

Tarsnap is ideal, but it's around $27 a month, versus $3.

[buro9]

It's a question of how much you're backing up... my Tarsnap use and cost is very low.

I retain off-site encrypted HDD images updated once a month of things like media which constitute the vast majority of my data and do not need daily snapshots.

[StavrosK]

Yeah, I want to back up my media as well (around 90 GB), but I want my backups to just work. Tarsnap would have been fine if not for the cost, so a tool that combines EncFS + SSH + rdiff-backup will be ideal for me.