You might start by asking some of the people that ask you questions, "Listen, I'm thinking of starting an additional business using this as one of my services. What do you think would be a reasonable cost for this advice?"

Let THEM give you an answer. Then if they come to you later, they are clear that there may be a cost of some sort.

Some may not like it at first. but, if you believe that you are GOOD at it and they find your information valuable, then they will create some way to exchange value with you. If not, then they are either not that committed to transformation. OR, you may have some work to do with refining your own value offering.