. $240 on Amazon, but you only have to buy it once.We've tried the Nest in two of our properties - the proprietary nature of their interface made them difficult to integrate with our management & monitoring system.That said, there are other thermostats which provide a minimum and maximum temperature (regardless of what the occupant chooses) at a fraction of the price (Honeywell, Braeburn and {I think} Sinopé provide models with this feature).   

We were definitely monitoring things daily especially since we had a 3-family flip of ours close on Monday.

I am working with a partner in Silicon Valley to develop a computer vision based security and monitoring system for multi family properties.

You could possibly get motion activated battery powered cameras (game cameras) to monitor property.

There's usually good locals that monitor it and can make good local suggestions.  

I was told I need to pay some company an annual fee to monitor it (surprise surprise ...fees everywhere). 

we are closely monitoring this unit and area but mostly have decided to exit this location by next year.

There are usually some good, local investors that monitor those forums.

This route is a little more expensive (cameras + wiring) as well as time intensive since you'd be monitoring the cameras, citing people, dealing with those people, trying to collect those fines.

This will make it easy for me to work on until its ready to rent, then when it comes time to rent it out I can easily monitor it's activity.