Based on about 200 visits over 3 years to all gay saunas that currently exist in Bangkok.
Most saunas are full of 40 year olds, but few 20 year olds. Considering there are as many 20 year olds as 40 year olds, and the 20 year olds have a higher sex drive, where do they go for sex?
It's a matter of luck (or waiting long time) which mood it is.
When I was in the army, I had night patrol with a boy from Berlin. He pointed out that there are so many stars in the sky. I thought he is gay, but a year later when I studied in Berlin and noticed he is right: due to electrical light everywhere, your eyes don't adapt to darkness and there is light pollution and you can see only few stars.
Some places have one price throughout, others separate prices for weekdays and weekend, time of the day (or rather night) and some have lower prices for young customers or higher prices for old customers (bordering on ageism in R3 sauna where over 50 year olds pay double price). Lowest entry price is 100 Baht (M-Place and Seed), highest 230 Baht (Babylon and Chakran).