$6.32 list price each from your local GM dealer. Less if you get a discount. p/n 88983035 My dealer can usually get them in 2 days if they have them in a local area warehouse. Yours probably could, too.
Of course, if you need them right away, I guess $30 isn't bad for a set from ebay.
I do find it interesting that the H/O did not have the insulators on the straps when I dropped that tank. And it had never been off. And I don't recall these on the 85 or 87 442. I'll have to look closer.
Nothing in the parts book about an Oldsmobile gas tank insulator either except for the X-body. Only thing listed for G is the gas tank straps themselves, p/n 557935. Maybe a Malibu and/or Buick thing.