You don't pay to pray ! My family Elders are often invited to speak ( at various gatherings & universities). As invited guests, their expenses are taken care of. People have expressed an interest in learning about the Lakota, and they have been invited to our homes to listen to our Elders speak about traditions, history, ceremony, etc. They are not charged a fee for this...they are our guests !
As for ceremony ( in this case Inipi - what you refer to as sweat lodge)...a fee is never charged. Someone makes an offering for the ceremony (tobacco, cornmeal), and states the intent (gratitude,healing, general prayers for the people, etc). The "pourer" does not get paid to do this. Everyone is fed, and if the pourer has incurred expenses, the "hat is passed " for those who want to help with travel costs (gas, tolls, etc). If the pourer needs to stay overnight, someone opens their home.
Simply put.....don't pay to pray...don't pay to be taught. Hope this helps.