This question is just food for thought, you don’t have to answer, but how easily can you get to the barn to pop a blanket on (and then take it of again!), and how many days between now as when his coat grows back would you need to do that? Or can you pay someone once in a while in a pinch rather than paythe monthly fee?
Also, is the horse in a basically open pipe corral or does he have three sides of shelter? And relatedly, can he stand in the sun when it’s cold but sunny?
I have a very woolly draft cross who spends part of the winter trace clipped and unblanketed, but we don’t get the fluctuation in temps from day to night that you have. We have huge fluctuations in temp but they usually last several days or weeks (And the weird thing is that it can warm up at night or drop during the day because the temperature comes in from Canada and Florida/Texas instead of just from the sun. It took a long time to get used to because I grew up in CA!) The upshot of that is that it is cool enough in the daytime that he doesn’t get too sweaty during the day, and we may need a sudden banker change but then usually it can stay on or off for days.