During the cooler season if your house is not in the mid 70's the cheapest most efficient way if you only have one tub will be 2 heat mats and 2 t-stat or 1 t-stat if you have the herpstat 2.

The other option is a oil filled heater to keep the room in the mid 70's however it is only cost effective if you have a room full a snake, for 1 snake it would be rather inefficient and expensive.