Say it with me again.

Band

Is

Curricular.

Not co-curricular (nearly nothing is co-curricular in Texas, people need to stop using that term, not that you did). Not extracurricular.

It is a CURRICULAR subject with an extracurricular component. That component includes concerts festivals and competitions.

It has a curriculum. It is on the TEKS. It is CURRICULAR.

The fact that it's an "elective" means literally nothing. It just means the kid chose the class - hence, "elected" to take it. It doesn't make it more or less of a class.

Legally you CANNOT charge a student to be in a curricular subject if they are on free or reduced lunch. Yes, this is part of why athletic budgets are so large - any of their kids that are F/R Lunch legally are required get free gear.

You CAN charge for the extracurricular portion. You can charge for competitions and festivals and trips. But you cannot charge for them to attend a district benchmark, for example.

Sticking to your guns in this case will only get you slapped down harder by any competent attorney who can argue the decided case law that exists and has existed on this subject for over a decade now. I can tell you now that your school district's attorney will tell you to back off and let the kid in, and they're right.

The kid has the right to be in the program. You're not required to bring them to All-Region if they don't meet your guidelines though, which may include private lessons.

This type of situation (legal issues) is literally the focus of one of the classes you take when you get your admin cert. Ask your principal.