Here are some other cheap options which I guess fall in the category of FIR heaters and are perfectly economical without the need for special "therapy" anything. Just point the heater at you while you read on the couch.
https://www.walmart.com/search/?page=1&query=infrared+space+heater&sort=best_seller
There's a lot of much ado about nothing out there with the outrageously expensive FIR home saunas and what supposedly makes them good for you. I think it's a lot of hype and the way they market them, they should have them tested like a medical device.
We're in a bind because if you just say to people, buy an IR heater and point it at yourself and you'll feel some pain ease away, then you're telling an "old wives tale" without scientific proof.
And if you sell someone a "therapy bulb" to help with arthritis in a special lamp, then you're basically selling a medical device. However, it's allowed because the person could just use a heating pad on their hands.
Both ways, no science has to be carried out. Certainly not the kind of science that needs approval from an Independent Review Board or FDA registration and approval.
So the only way to make people believe your product is good is by making it fancy and raising the price. The "official" sauna is supposed to be better. But when I ask "how is it better?" I don't get a real answer. I'm also very suspicious of documentation that tells you to use eye protection, and then fails to tell you how long to use the therapy device. It directs you to ask your "health practitioner." That sounds like nonsense since in the 1970s and 80s, every bathroom came equipped with an IR light in the ceiling and a timer switch so you could keep warm while toweling off.