So I went to price out some hot tubs. These things are crazy expensive. Wanted $15k plus $2k to wire it up. Have priorities and a hot tub isn't one of them. Was in shopRite food shopping and I see a blowup hottub for $350 bucks. I was expecting this thing to be crap but it is awesome. Powerful bubbles and stays hot. Highly recommend.
*Not my pic but same tub.

We bought a spa like this last yearand it's been awesome. Like you, we were shocked at how much they wanted for traditional spas. I just cleaned and refilled ours a couple days ago, so it's funny you posted about it! In the summer we don't even heat it, just run the filter occasionally. Plus, it's 250 gallons of water in case of emergency. ;)

I didn't like the idea of using harsh chemicals and chlorine, so instead found a great alternative product from Purest Colloids called "Hot Tub Silver". It turned our spa into a healthy mineral bath. I just pour a whole bottle in each time I change the water and that's it, have never had to add other chemicals and water is always clear. Amazing stuff, a very concentrated form of colloidal silver that kills bacteria and fungus on contact and prevents algae growth.

https://www.purestcolloids.com/hottubsilver.php

Wonder if you can use that stuff in a big above ground pool.