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The first month is always much higher than subsequent months. 8-)
There are so many factors.What is the cost of your electricity? What temp do you keep the tub at? How often is it used? Jets on? Jets off? Bubbler? 60 amp? 50 amp?$60/month could easily be at the high end of normal for a Sundance.
I am curious why do you say normal for a Sundance and also would not the model play a big part. The Maxus would be the only model I would think they make that could run that much but that is a much larger tub than most others.