The heating of it mKes it expensive. I think a pump running has to be added also

In California this is a hot topic, so the industry had to comply by making units much more efficient. I was able to estimate approximately how much energy would be used by this website: https://cacertappliances.energy.ca.gov/Pages/ApplianceSearch.aspx    The less expensive hot tubs cost much more to run than the more expensive energy efficient models.

The answer to this also depends on where you live and the ambient temperature that your hot tub operates in. There are much more efficient hot tubs on the market that are designed for cold weather operation. These usually have thicker, more advanced insulation systems and often are designed to recapture heat generated from the circulation and booster pumps by employing a perimeter insulation instead of a "full foam" insulation which often places the filtration equipment outside of the protected inner cabinet. In my area a high end hot tub would be expected to run about $30 / month for heat and electricity. This goes up the more you use booster pumps in the tub. An older and much less efficient model might use $100 per month. Keep your cover in good condition. A lot of heat is lost through there. When the cover feels heavy the foam is compromised and you should replace it right away.

NW Indiana - 10 years and year round use- average costs for us 12-15 dollars a month in electricity. 5 person with insulated cover.