So, Stagedoor Manor is not the only place the casting directors are going to look for talent. I'm sure they also went to performing arts high schools around the country.
In addition, I totally understand your frustration with how expensive these summer camps are, but there are PLENTY of talented kids who never attend summer camp and go on to be successful performers. There are lots of ways to provide training for your child and none of them are particularly cheap. Private singing lessons, dance lessons, acting classes, headshots, trips to NY for auditions, coaches, etc...all add up and make being a professional kid a very expensive endeavor. If having your child in show business is a financial hardship for your family, perhaps it is not the right time for your child to be pursuing it. I know plenty of parents who have told their children that they can pursue acting after they go to college or major in it in college so that at least they are at the age where they can get part-time jobs to help support themselves.
I also think that if you have a child who is itching to perform and train, there are always ways of finding "community" classes, free training, free headshots, and performing opportunities in community theatre. Money should not be the reason not to pursue a dream - even if it is the reason to not attend summer camp, which is a privilege, not a requirement.