Currently, one can buy 8G DL DVDs for storage ($0.33 per Gig), and external 1TB USB HDs as another option ($0.10 per Gig.) Is there a midrange technology, say 500G or so, perhaps tape-drives in a useful price-range for the consumer?
There are numerous options in between, yes (including tape drives).
You mentioned tape drives. Althought not so popular amongst home users, they've always been there and used. I know some people who swear on them when it comes to backup. Not so cheap nowadays thought.
A general article on backup solutions here.