Update: It looks like the Nexus 6 (which is actually in stock right now, at approximately 12:45 AM Pacific) and the Nexus 9 are also eligible for the $50 Play Store credit. Add the G Watch to your Play Store cart to see the $99 price.
Have you been waiting for a super-cheap Android Wear device to get your hands (wrists?) on the platform? Then this is it.