I'm in the camp that you shouldn't charge the school for work that YOU do. You're the employee, other duties as assigned, etc. But unless your spouse is also employed in some capacity with the band program, they shouldn't be writing guard work for free. The district is paying YOU, not your spouse.

My wife is also a teacher, not in my district. If her school asked me to write drill or arrange music, I would be happy to do so - for a fee.