admittedly not exactly the same product, but certainly in the same ballpark (server consolidation/management), compare the price to VMware vSphere, a hypervisor for servers. Standard edition starts at 995$/year (83$/mo) per physical CPU.

vSphere is an older, more mature, and more featureful product, but the core value prop is the same: save capital expense by consolidating your services into fewer physical servers, with improved manageability, through virtualization. arguably, docker can enable denser consolidation because virtual machines have typically higher cpu and memory overhead compared to containers. so comparatively maybe docker is underpriced?