I think I'm understanding something wrong. What error did I make below?
Filecoin$0.0292 / TB-Month
Siacoin
$4.29 / TB-Month
Amazon Glacier
$4.00 / TB-Month
It does look like things have changed since I noticed what was up a little.
What's most relevant is that the fact that these chains ever let data expire is simply an artefact of their design: they could be changed to never let anything be deleted ever, and still pay people for storing it via mining and fees.