Sad to say, moving always costs more than expected.
The winter we have been enduring this year is particularly COLD, certainly not typical. Since it is so cold in the garage, I suggest that you install some kind of radiant heat in the floor. It'll cost more initially, but the garage will be usable in the winter. I'd say hot water radiant heat, but then you have to install some kind of water heater. If you can afford to put a tile floor in, you can put electric radiant heat in. If that's too expensive for the entire room, then put some kind of radiant heat where you sew and/or in the most used path around the room. That's what I plan to do when we remove the ugly carpet from our bedroom and replace it with a beautiful hardwood.
I've read that some people have used insulbright as backing on curtains to block the cold and the heat and that it works well. You could also make a little foot warmer bag (with insulbright batting) to use when sewing.