What's the most extreme cold/hot they can live in?

I'm moving from now a very HOT climate to a very COLD climate. Here I used an AC in the summer to keep temps a little below 80 and have done nothing in the winter so far and night time temps drop around 40 SOMETIMES in the 30's but I don't think it's been that cold at night. I have SUPER production right now. My asf's are banging out babies left and right and so are my mice and rats.

Problem is, where I am moving, right now night time temps are around 7 or 0 and daytime only gets about 30, although tomorrow's high is around 12!

I'm guessing that would be WAYY too cold for them. How would you suggest heating a detached garage to a decent temp (something they can live in) without breaking the bank?

Is it even necessary or as long as there is no direct exposure to wind are they OK?