Jin,
I don't know if this is an option for you, but if you can call credit card companies or banks and get a low or no interest loan (no interest for 9 months, etc) it MIGHT be less expensive to buy the whole sauna. The payments might be around $100 a month, maybe $200. Mine are a bit above $100 for the credit card loan. But any place I could have found around here (especially when you add in gas) would have cost more.
I did hear about one person tho who found something for only $50 or even $40 a month for unlimited use. I forgot who it was now, lol.

If you could find something like that, then that is a GREAT option. But I was not able to find anything similar here in Southern Cali.