mine is an older tub, so higher capacity than some of the more modern ones(deeper foot well etc), its 2.2m square and seats 6/7
costa about £35 a month to run on electricity, we are normally in 2 -3 times a week, like it at 39c and drop it to around 29 in standby, filtration pumps runs currently for a bout 6 hours a day,
as its an older tub the foam insulation is not as thick as the modern tubs, but the cabinet is stuffed with bubble wrap, we have a very good quality thermal cover.
I am hoping to reduce this with better pump management, and boosting the standby tem in the middle of the night when we are economy 7.
I have considered both a heat pump , but these can be a bit noisy , and a log burner.
I like the idea of a small slog burner, but not for day to day use, it would come in very hand and be a cheap way of getting fresh water up to temp , at the 8 weekly drain and fill , would really need to have a stainless steel heat exchanger ...
and chemicals and filters are around a fiver a month
hope this helps