Considering the ridiculous amount of money you may be about to drop on watching Thor: Ragnorakin IMAX 3D, it's about time you got something for nothing. For one day only, Amazon has you covered.

In a little-noticed "Thorsday" promotion, part of a wider sale on Marvel comics you can read via the Kindle or Comixology apps, the online retailer has dropped the price on three collected editions starring the God of Thunder. Two of them are even good ones.

Thor: Volume 1is comics veteran J. Michael Straczynski's reintroduction of the character from 2007. It's one of those great jumping-on points for people who are intimidated by superhero comics, since it basically invents a brand new incarnation of Thor (who promptly builds a copy of Asgard ... in Oklahoma.)

Thor: God of Thunder Volume 1: The God Butcheris a 2014 collection featuring no less than three incarnations of Thor; it offers some pretty deep insights what it means to be a god. And then there's Thor Visionaries: Walter Simonson Volume 3, which ... why would you give away the third volume in a series?

At least it seems to be a smart Amazon strategy to give away those other first volumes -- because no doubt you'll want to keep reading when they're done, and the second volumes are on sale in the $2 range.

The structure of the rest of the sale, however, is confusing in the extreme. For example, the first graphic novel collecting the highly-regarded Ms Marvelreboot appears to be free -- but only if you're paying for Kindle Unlimited or Comixology Unlimited subscriptions. It's currently $1.80 to the rest of us.

A bargain regardless, but still -- Amazon would doubtless have more success with the promotion if it made clear what you're paying. In general, hooking readers with the first collection in a widely regarded series makes so much business sense that we wouldn't be surprised to see the company doing more promotions like this in the future.