There isn't any fee for using the health club facilities. However, at SSR, it seems that there's some sort of day fee for using some of the changing area, like the inside whirlpool, I'm not sure if there's a sauna there too. My DSis had stayed in '08 and it had been free to use that changing area, but people have reported that there's now a day fee. I don't know much about that.
No fee for gym use, but I was told that to use the sauna (at SSR) you had to pay something.. which aggrevates me. 'cause at AKL you could just use it at your leisure