Camps are usually pretty cheap, especially if it's a one day camp. Where it becomes expensive is hotels, airfare, and rentals. If the school is close enough where you can drive it then go for it. If not, establish some dialogue with the coaches and feel out the conversation. This is where having a good travel coach helps big time. He'd usually get the 411 before sending you there.
What I would be doing is making sure all these coaches know that he hasn't really pitched. Even if he fails as a pitcher, falling back as an all state catcher is always a pretty good safety net. Don't worry about them coming to see him multiple times. The school 2019 committed to came 6x before even a hello. How is his bat? A top of the line catcher in his state should be getting attention by now. When the P5 and mid majors ask what other schools he's talking to - do not mention the D3s.