How cold is too cold?

Sitting here at my dining room table, wearing two sweaters and slugging hot coffee, I'm practically shivering. Why? $250 to PG&E last month, that's why. This giant rented box we're living in, with its single-pane windows and shoddy construction, is a sieve, and there's very little we can do about that. I've set the thermostat to 66. In the master bedroom, we've put a plastic sheet -- the kind you shoot with a blow-dryer to seal -- over the bathroom window. The vent in there is busted, so I use a space heater when I'm showering.

We can't put in new windows. We're stuck here more or less indefinitely. The males of the house don't seem bothered by the chill; my husband is content to put on a sweatshirt. Should I pick up some cheap longjohns? Or admit defeat, turn up the heat, and find another way to save cash? The new $2 wine at Whole Foods is half-way decent...