There are cheap Hydrofarm thermostats on Amazon. $28 last time I checked. I had one while I was building up the funds for my herpstat. I bought three just in case.
If you want something now, which I think is better than later, I heard you can go to a hardware store and look for a lamp dimmer or rheostat. I hope someone could elaborate more on this.
Also you can keep them warm by cranking up your own thermostat in your house if you can. I bought a $20 small room heater and just point it at my bp. There is also the hot water bottle trick.
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