I have a hot tub in the sun room, not outdoors but with skylights over it and and crankout windows on the south side. Great for the aching back and knees (my wifes).
Operating costs are one heck of a lot less than the pool, my guess that the electrical cost is about $12.00 a month. Go with a 240V system instead a 120V source. Some reason it is easier on heaters
Repair costs? In 14 years I have replaced one pump, one heater, two heat sensors and about one gazillion light bulbs. As long as your eyes are good most of the repairs you can do yourself if you can read a wiring diagram and use a screwdriver and meter.
Chemical costs are negligible. I went the full technical route first with chlorine for a couple of years, then changed over to the non-chlorine stuff (Baqua-whatever). THEN I paid attention to the repair guy and now I add about 1 tablespoon of good grade granular chlorine a day, shock it with non-chlorine shock once every week to ten days and change the water every two months. Do I enjoy it? Well the wife does, I like it better than the pool. Would I buy another? Probably not unless I could get a Doctor's perscription and write part of it off, but I am turning into a cheapskate :-) Usage drops off with the relative newness, but it still gets a lot of use, especially when the outdoor temperature drops. Cat hates it, Scottie is going to fall in one of these days. If indoors you need to be able to vent the area to avoid humidty build up.
Rick Hasn't improved my modeling one darn bit.