I'm looking for the best method to store a backup of important files and 5+ years of digital photos that is safe from some type of fire/flood disaster in my home.

I'm looking for:

• Affordable: Less than $100/yr or first-time cost.
• Reliable: At least a smaller chance of failing than there is of fire or flood
• Easy for initial backup and to add to, and at least semi-easy to recover.

I recently purchased a small home safe for physical vitals. It was inexpensive, solid, and is fire/water safe. If I had a physical copy of the digital files, the safe would work fine for this, but I don't know what to store in it that adequately meets the requirements above.

• Hard drive - I read that the danger of it not spinning up makes a hard drive a bad choice for this type of storage, although it was my first thought and would definitely be the simplest choice - very easy to take out once a month and add files to.
• DVDs - Way too much of a hassle for both backup and restore.
• Tape - No idea on the affordability of this option
• Online - Given that I have at least 300GB already and ever-increasing megapixels means ever-bigger files, and my ISP upload is about 2Mb at the best, this just doesn't sound like a good option for me, but I could be convinced.
• Other - Have I missed something?

Also, I'm already covered both for sync between computers (Dropbox) and a nightly backup of these files (External HDD). The problem with the nightly backup is obviously that it's always with the computer and in a disaster would be destroyed along with it.

Is anyone else doing something similar? Is the HDD as poor of a choice as I read, or is it a feasible option? Maybe two to reduce the likelihood of failure?