The answer to your question is, "It depends."
Not all spas use the same amount of electricity. Even if the spas all started off with water the same temperature and the same environmental conditions they would all use different quantities of electricity.
The Variables
Water capacity- It simply takes longer to heat up 500 gallons of water than say 300 gallons.
Insulation- Spas with little or no insulation do not keep as much heat in as fully foamed or full insulation. The increased heat loss will be made up by using more electricity.
Spa cover density- the lighter the cover-- the less heat retention.
Some argument may be made over 110v vs 220v configurations. But basically they cancel each other out... the 110v models have a longer heat recovery time while the 220v use higher wattage heaters.
The bottom line-
A premium spa can cost as little as $12.00 a month to run. OR $6,240 over ten years continuous use.
A parking lot sale 'deal' can cost upwards of $50.00 a month to run. OR $26,000 over ten years continuous use.
Now see why I make such a big to do over insulation?
Happy Tubbin'