My electric usage for this Nov compared to last year before we got the spa went from about 1100 kwh to 1344 kwh, but we've had a much warmer year and actually ran the A/C until about a week ago. So it's hard to say how much of that is due to the spa.
I really don't think they draw all that much power, as they heat so slowly. My guess is maybe comparable to a couple of 100 watt light bulbs left on full time. I should get one of those gadgets that you plug into the socket that measures power consumption.
Have you looked at the Intex manual? It may give the power draw in the tech specs.
BTW, mine is doing to get tested this weekend for sure, as we're supposed to drop to near zero Saturday night.