[ABMX]

The secure aspect would really vary by how paranoid you are about your data. The closest to 100% secure options would be anything that never transmits over the internet and is in your physical possession and control, like the CD/DVD media and (assuming no viruses) local private file servers or hard drive arrays. Next would be encrypted backup solutions that run their backup systems via some sort of VPN, and/or building your own where only you can touch either side to configure the encryption.

By cost, CD's are only a few cents a piece, DVDs not too much more per need/use. A local terabyte hard drive can run $80-$120 and is likely to last you a while on the size part of things(guessing from the fact you're doing backups with DVDs and pen drives). Grabbing two drives and RAID card for RAID1 can get up to a total of $300-$500 depending on exact parts. Creating a local dedicated backup server can start at $700 easily. Colocating the same server could cost the price of the server plus whatever monthly price the datacenter charges plus data overages. Renting a dedicated server or VPS would probably be cheaper then that.