My thought process was, when deciding whether to go to a camp and spend money, to not have any regrets and what-ifs (still left with a couple) when the process was over. And I'm as frugal as they come.
Perhaps your gut is right, but the P5 has taken the time to see your son play and you got an invite. Yeah, it may not work out, but what if it does.
If you sign up, I would have your son text the coach to let him know and push the dialogue.