Combine an old PC with a couple of biggish drives (you can use a PCI SATA card if you need it) with FreeNAS (
FreeNAS: The Free NAS Server - Home) and off you go.
Store your stuff on HDD0 of the FreeNAS server and set FreeNAS to do an rsync to HDD1 daily or weekly or whatever.
Easy, reliable and cheap.
