Hi David,
I'm in central California, and I keep my reef in my garage. It is a standard, uninsulated, unfinished garage.
Our temps last winter got down into the 30's, which is unusual for here, but probably warm for CT. I was able to keep the temp consistently at 73, which was my goal, however it was very expensive. The electricity costs were significant.
The temp in my garage averages, probably, in the low 60's to low 70's in the summer, and probably low 50's to mid 60's in the winter, except during that cold snap we had. I don't have a problem keeping the tank warm. I use insulation on the side, back, and bottom, and have thick acrylic from Home Depot on the top. Two sides are visible.
In the summer, the sun shines right into the tank and this warms it up. I can avoid this by using blinds, but I actually like the sunlight going into the tank. This does raise the temp, but you could avoid that with a chiller quite easily.
Right now I run the tank at 68 to cut down on electricity costs.
I don't keep my cars in the garage, but I wouldn't expect that to be a problem if you avoid idling them excessively, obviously.
Hope that helps.