A trip to the sauna is excellent for skin health because it helps flush out toxins and it can rid your skin of bacteria in sweat ducts and the epidermal layer.
I’ve visited a few saunas in the Bay Area. I can confidently recommend two excellent places for private saunas rooms at affordable prices: St. Pierre Massage and Spa and Watercourse Way Bath House Spa.
In Napa Valley, private sauna visits cost $15 per visit in the 5 visits $59 package at St. Pierre Massage and Spa. For two people the cost is $60 to reserve a private sauna room for one hour. Inside the room, there are two separate private sauna booths that share a small common area, where there is a small table with dried mango snacks and water to enjoy during your visit.
What I look for in affordable spa care is cleanliness and standout customer service and this place has both. I like that there is no dust or cobwebs in the corners or on any furniture. The bathrooms are up to par as well. The waiting room has a fireplace and water feature for optimal relaxation. Also, the waiting room is far enough from the reception area that it feels tranquil and quiet away from the hustle of people entering and exiting the spa.

https://www.stpierremassageandspa.com/facials.html
Another excellent spa with affordable luxurious sauna spa packages is Watercourse Way Bath House Spa in Palo Alto, CA. This spa offers private sauna rooms with a hot tub starting at $40 per person, per hour. For the first reservation, they require a $40 reservation fee which is then deducted from your payment at the spa.
The total is $80 for two people in a private hot tub sauna room, $20 more than Napa but there is the bonus of having a hot tub too. They also offer massages and facials inspired by the season. The December package is Sugar Plum Cranberry with a scrub, facial, and massage for one hour and thirty minutes for $143!