If a judge is going to slight you at the region level for not having a traditional uniform, they shouldn’t be judging AND all of our more wealthy friends would be screwed because they’re eschewing traditional uniforms for costumes. As long as the band is uniform in appearance, it doesn’t really matter what uniform they wear.
Also, invite (and gently insist) that your Super, CFO, and anyone else you can think of attend the event. If you can, go early and let your kids (and your admin) watch the other groups. The kids will learn about performance execution and the admin will learn about appropriate funding and support. Bonus points if you can get them into conversation with your region exec sec or admin from a successful school.