Most works are normally from referral.
I would solicit the high school band director(teacher) and let them know your service and what you do. Let them know that you are accomodating choirs and school bands and that you give special rates for them since 'you believe in what they do and the future of music'. I think that 'reasonable rates' for high school is $50-100/hr for a recording (usually 2-3 hours)
Usually they will hold the master at the end of the recording when they hand the money to you. Have a few backup and let them know that if they want to cut it to a ready to release copy, they can for additional fee. (tracks, mastered)
Most schools actually didn't know on these services or they didn't know that some of them are affordable that they didn't include these in their annual budgeting. Solicit schools during their budgeting season (fall?) and see results within the next 12 months.
All the best!