Research firm TechInsights has done a teardown of the Moto G and made estimates based on the components of the device. From the looks of it, the 16GB Moto G costs Motorola (read: Google, since Google is the one footing the bill) about $123. Motorola is selling that model at $199, which means just $76 of profit on each device sold.
Sanford C. Bernstein & Co. analyst Mark Newman has estimated that once you add in other costs surrounding a device, Motorola may be making just 5% operating profit on each Moto G sold. For comparison, Samsung tends to make between 20 and 30% operating margin on its devices, and Apple is getting between 30 and 35% on its iPhone 5s and 5c.
Of course, this is the benefit of being "a Google company", you don't necessarily need to worry about profits on every device as long as you have a plan. And, gaining market share in emerging markets with quality devices is a solid plan.