Each of the 3 apartments have their own thermostats.

Nobody else can say what your mortgage is going to be, what cable package you're going to pay for, what extras (or not) you intend to provide, or if you go with the cheap thermostat so guests can abuse your HVAC or pay $200 for a smart one where you can set temperature limits.  

@Mark Fries is right, I got 1000 sq foot home AC for 3400 and the duct work for $3200 with new vents and 12 month supply of filters with digital thermostat.

@Ray B.Meanwhile.. do you have a lockbox on the thermostat?

Louis...it rarely gets cold enough to really need to go all the way, and there are additional, knock-on effects involved in turning off heat to a place for a long time that you can avoid if you just keep the thermostat at 55 degrees and, when the coldest weather is projected, you set up the lowest faucet in the place to the slowest steady run for the duration of the coldest temperatures.

I have covers on the thermostats but the tenants find ways to get in them and raise heat and lower air conditioning in the summer.

(Link below)Some of the things I'm looking into is rebates on thermostats, rebates on energy efficient appliances, hopefully some rebates and 0% financing on a new a/c unit and insulation. 

Mine can set door codes, message (or call) guests, schedule cleaners, adjust the thermostat, monitor my cameras, & call a plumber just as easily as a local PM can, for 1% of the costI wrote much more about leveraging offshore assistants in this post here.

They’re saying they’ll do it for free this time but normally have to send a technician which is minimum $45.Alternatively, I could have the contractor go to their office to get the key and then subsequently return it.At the beginning of winter, I was charged $90 for a technician to replace the batteries in a thermostat.

Said everything was fine so I handed him the keys.The very next day he started calling and texting complaining about how everything was broken and he would need me to pay for a new washer, fridge, CO detector, thermostat, shower faucet, screen door, and blinds.