You've got a couple of things that go into the question of "what is an acceptable rate?"
1) What will the market bear? How much demand is there for the material you have to teach? How much demand is there for you specifically? How much competition do you have?
2) How much do you have to charge for it to be worth your time and energy? (This is a personal question that only you can answer.)
If the answers to #1 and #2 overlap, then congratulations! You're in business.
I currently charge $50/hour for private lessons. Factors that go into that rate are as follows:
I have 33 years of martial arts experience + black belts in BJJ and a couple of other arts.
I have a reputation as being a relatively good instructor.
I am not a great competitor or tournament champion.
I teach out of a school that has several BJJ black belts as well as other skilled instructors.
Our student base is not particularly wealthy, so $50 is a significant chunk of change.
I have not spent much time or effort marketing myself as a private instructor.
I have a regular day job that pays the bills
I enjoy teaching.
Question... What if any application does Ho Sin Sul bear in anti-grappling? As a BB in BJJ, you are right where I want to be. After 22 years working in TSDMDK, and just now heading to the mats, I am very curious.