We are peers, if you appreciate my input then I have a point of view which is as valid as yours. Therefore, we are equals
Accordingly, my charge out rate to you is the same as the rate you charge to your clients
So, if you want to use my services you pay me your charge out rate for the number of hours that we work together
As a matter of consideration, it's also good if you also pay me in the same amount of time that you prefer to be paid by your clients...