One price-point that would be very understandable to me is charging more to bottom for anal sex. Not so much for the in-session act as for the additional prep-time before the session. Paying (or not) for that additional time and effort seems very reasonable.
There are a bunch of local and regional groups on FetLife for massage exchange.
I remember a dedicated message board website for massage exchange. I tried it, but almost every listing was overseas or a long distance from me.
I love Judo. I competed in Judo in my early twenties and loved it. Even thirty years later, I successfully pulled off a safe landing when I took about a ten foot fall by accident due to my Judo and Japanese martial arts training when I was younger.