Sorry if this has been covered already, but why don't you heat the room?
I run a 50+ tank fishroom and maintain the house (via thermostat) at 72 degrees in the winter. I keep the fishroom (which is in the basement) doors closed and heat the big tanks (180g and 2X150g) with a 300W heater each. The room stays ~74F (lower for the tanks closer to the floor), higher for the top rack of tanks in the winter.
This is plenty warm for most Central American cichlids and a lot of other "tropical fish"...
My total electrical bill for the house is ~$200/month in the winter (add another $120 or so for Natural Gas)...
Also, you could try Uruguayan fish - Gymnogeophagus, Chanchitos, Pikes, etc. - they're neo-tropical and actually enjoy temps in the 50s in the winter...
Matt