I don't notice anything during the summer, and I have a good 24 feet of flexwatt running. It's the space heater in the winter that I notice, but it's only $20-$30 depending on how cold it is outside.
And for the space heater hatersI use my space heater at full power in the really cold months, so roughly 2 months straight when the temps are in the single digits or less. The snake room is in my basement with cement block walls, and no insulation. Still the bill is only another $20-$30 a month. But you have to keep in mind that different areas get charged different rates. For example our monthly water bill was $19 a month when we moved in, now that I have a billion rats that go through 10 gallons of water a week our bill is still only $30 a month.