One thing to caution!!!
Unless you already know the wiring of the old thermostat, do NOT assume anything. Your 1 hour for thermostat install, could turn into 2. Or a lot more if you are not up to speed with HVAC systems and controls.
Also, you didn't mention anything about the time to set them all up in the Nest app (on a customer's device) - which inevitably they won't remember any passwords for anything creating hours of additional waiting and fumbling around.

Yes, your price is to low!

Me:
1) Average .75 hour per device, .75 hour setup & cleanup, 1 hour programming and demonstration. That's 7 man hours. This assumes compatible wiring at thermostat and compatible system. This also assumes good wifi & network already in place.
2) Make SURE the customer understands the wiring at the thermostat (or type system) could cause additional labor or no installation at all.
3) Make SURE the customer understands most people's networks are BS and can cause problems with installation and future function. And that an upgrade of the network might be in order.
4) Make sure the customer has ALL their info ready ahead of time. And all devices to be programmed are fully charged. Failure on their part to do all of that, will result in additional hours of labor. Make this point VERY clear to them before the appointment.