We are a large team, and we host a large meet every year, which is put on by our booster club and the parents. Through this meet, we are able to keep dues (ie: all competition expenses) way down, much lower than gyms in the surrounding area.
I love having a booster club because when we raise funds we, as a separate entity from the gym, can decide what to do with it. We are not at the mercy of what the coach wants to charge for things like meet entry - all of those costs are paid as advertised and there is transparency to the parents upon request. Our coaches are paid an agreed upon amount for meets, travel and expenses, including to our home meet. Judges for our meet are paid fairly and consistently regardless of where they are from. We are not obligated to pay for any gym business expenses - in fact because we are designated as a 501c3, we are strictly forbidden by law for paying for things that benefit the business operation such as equipment. No imaginary mats, no slush funds. It is all out in the open, and the BC doesn't make money as evidenced by keeping a very low balance year over year. Everything that is raised goes right back to the member families.
I agree that an open an honest conversation with the coach is the only way you be able to judge their motive. First, I would want to know exactly what benefit they hope to get by moving the meet in-house? What do they hope to accomplish? Maybe your coach has a valid concern that we are all overlooking here.
In my experience, the best way to avoid this issue, and the most fair for all, is for the gym to charge the booster club a flat rate for "renting" their facility to use at the meet, just like any other facility would do. Rather than collecting your admission and entry fees, which is the main profit, and completely unfair to the working parent volunteers. We went through this with our old gym, and our parents were very upset as well. This is how we solved it. Ultimately, if your gym has only 18 team members, the coach NEEDS you all to keep their business up and running!