TL;DRGoogle and Back Market are selling $3 USB keys that come preloaded with ChromeOS Flex.The keys simplify getting ChromeOS up and running on older hardware.These new keys are out of stock as of publication.Last month, Back Market and Google introduced a low-friction new way to get some extra mileage out of older PCs and Macs: ready-made ChromeOS Flex USB keys that make it simple to get Google’s desktop OS up and running on computers that are out of software support or struggling to run heavier operating systems. Those USB keys are now up for sale — and they’re surprisingly cheap.Google announced availability of the new USB-A keys in a blog post. They’re being sold through Back Market for just a few bucks, and come with simple instructions explaining how to use them to boot ChromeOS on a Windows PC or Mac.