Like most people, I'm not doing offsite backup of my data. Are there any low power/cost end to end solutions that I could plug into my friend's home network and backup data from my home?
You can easily tunnel rsync over SSH. You can configure even the simplest routers to do port-forwarding, e.g. your friend's external IP on port 2222 is redirected to port 22 on an internal host.
Rsnapshot (rsnapshot.org) is a free rsync-based backup system; it is very efficient in terms of disk space and keeps full backups, but only keeps 1 copy of each file.
you might be able to use local-drive backup software, a drive at your friend's home, and a pogoplug device to access the drive remotely as if it were a local drive.
http://crashplan.com/
Cross platform (Mac/Win/Linux/Solaris). Some extra features unlock if you buy the + version.
If you want a totally free solution that would take a little more work to implement, look at Duplicity:
http://duplicity.nongnu.org/
rsync based, uses SSH/GnuPG for security.
Run one of these on whatever hardware you have available.