If you haven't gotten your hands on a Cardboard VR viewer via one of the many third-party companies making them or through one of Google's own time-limited promotions (or you're not interested in clogging your arteries for one from a McDonald's Happy Meal), Google will now sell you one directly through its online store. In a listing that went up recently, Google is offering the Cardboard unit for $15 for a single unit or $25 for a two-pack. It appears to be the same Cardboard unit that Google introduced in May of last year and should be compatible with most phones under six inches in size, including the iPhone.
The listing is a part of a new Virtual Reality section in the Google Store, where Google is also selling Mattel's new View-Master VR starter pack for $29.99. Mattel's unit ditches the paper construction for a plastic housing and more robust lenses. A third option in Google's store is the $14.99 Goggle (not Google) Tech C1 Glass, a foldable plastic VR viewer built to the Cardboard spec.
Google is hosting its big developer conference in May and it's very likely that VR will play a big role there. If you want to see what all of the fuss is about before then, you can have one of Google's Cardboard units in just a few days if you order now.