About a papa (a male supporter) who keeps trying to recruit me into his religion

I’m having trouble with a papa (a male supporter) I see regularly because he’s very easily influenced. He was originally health-conscious and drank two liters of water a day, but after his spiritual leader said, “Drinking too much water is bad for you,” he stopped drinking water. As a result, he said, “I used to wake up during the night to use the bathroom, but now I sleep soundly until morning!” I thought, “You’ve simply reduced the number of times you go to the bathroom,” but I just brushed it off by saying, “What wonderful teachings.” After that, he started saying things like, “The air where you live isn’t good! The air near my house is clean, so you need to move! Otherwise, I’ll cut ties with you!” and pressured me to move. He’s very stubborn once he gets an idea in his head, so I said, “Okay,” pretended to move nearby, and let it slide. Apparently, he’s also spending tens of thousands of yen on memorial services for my ancestors and protective charms. It was fine when all I had to do was listen to him and I received my allowance, but recently he brought me an enrollment form and started insisting that I join too. The enrollment fee, annual dues, Bible, prayer beads, and other things would cost over 100,000 yen. I don’t think I can go along with that, but even when I say, “I’m a Christian,” he insists, “Christians can join too,” and won’t listen. I also feel awkward suddenly telling him, “I don’t believe in your spiritual leader.” He isn’t recruiting me to make money—he genuinely believes it’s a good thing. He’s extremely stubborn. I want to continue seeing this papa (a male supporter) on a monthly arrangement, so could you suggest a good way to turn him down?