Best choice for long term external storage?

I'm looking for a trustful method for offline (external) storage. I used to save stuff in 4 GB DVDs because they are cheap, although have very small storage limit for nowadays standards.

If I go for external HDDs, I'll probably have to buy a NAS or something, so I'm considering go for DVDs again. Are they considered reasonably trustful?

Any suggestions, considering I'm look for a not very expensive solution?