MO-DISC (or Milleniata) discs are what I use for offline storage. They're not THAT expensive - I only do a backup onto them once per year (Time Machine to an onsite server for everyday), and so far my wife's annual output of photos and video can be coaxed to fit onto a box of 10 DVDs, for roughly $35-40ish
I put 'em in a fire-resistant waterproof portable safe hidden elsewhere on the property, and consider myself safe from lightning/flood, theft and a few similar gotchas. I originally had a plan to put a wee server in at a friend's house several km away, and do reciprocal backups that way. But it's only recently that the bandwidth for that has been affordable (in Australia) and the above solution makes me feel safe enough that I haven't gotten around to it.
I don't need them to last 100 years, I just don't want to be surprised by bad DVD+R dye or whatever in 3-5 years as has been the case with other types of burned discs. I've never been able to get a straight answer on how long burned DVDs can be expected to last, but the MO-Disc people claim 1,000 years and I'll be happy with 2% of that.
If DVD readers go away in a decade, they won't go away WITHOUT WARNING - I'll have time to move data onto holographic crystals or whatever replaces them. After all, we can still buy floppy drives and VHS tape decks and vinyl record turntables... Plus I can also put everything we've done onto a 500GB drive and toss that into the fire safe, while I'm at it.
I've been doing this for a few years now and so far all the earlier stuff remains readable when I pull 'em out every first-week-of-January...