Your HS kids don't need to be playing on school provided pro line instruments IMO. Nice step up horns do just fine and you can get a lot more in the same budget.
If you are close enough, we've had great luck with the Orion instruments from The Bandwagon out of Fort Worth. We've liked their trombones, trumpets, and tubas. Their horns are okay but I'd stick with the YEP 321's for your euphonium needs.
You can also request specific mouthpiece pairings. We get all of our trombones from them with 51D mouthpieces and our trumpet teacher always gets 5Bs for his beginners.