What will this spa cost to operate monthly?
Energy efficiency saves. Portable spas can be much more energy efficient than built-ins, but ONLY if properly insulated. That insulation as well as the insulating value of the cover will be the key determinates of operating costs. The most energy efficient spas are totally foam-filled. Think twice about spa companies that suggest stuffing "Pink Batts" or something similar underneath the spa skirt. (It should be done with the spa construction).

We use multiple layers of high-density, closed-cell polyurethane foam, like a commercial freezer. Closed-cell foam is water repellent while open-cell foam can absorb water, which reduces its insulating value.

Some spa retailers suggest that a totally foam filled spa will create problems if there is a leak. Treat these companies with caution. Wright Spa pools have built many spa completely surrounded with concrete and tiles. These would cause some problems if they leaked but our quality control gives us the confidence to put the spa anywhere. A company that wont provide a foam filled spa because a leak would be hard to fix may not have a very high quality control system in place or lack in their servicing skills.

Operational Costs
Reputable dealers will provide documented information on typical operating costs. Heating costs for a spa with low initial purchase price can run two or three times more a month than for well insulated models which may cost more initially. With higher monthly operating costs every month, the total cost of the bargain spa can add up to more than that of the better made, well insulated spa. Don't take the salesperson's word for operating costs. Ask for the estimated costs in writing, and ask for a referral you can call to check what their experiences have been.