$600 for a school bass? I envy you. Back in high school, the only bass the band had was a horrifying mid 90's squier affinity p bass which looked like it was repeatedly bashed against a brick wall. I dunno whether that bass always played awful, or whether father time's assault caused it. I can say that the band director was glad that I brought my MIM Jazz to play instead...
If you go the 2 bass route, I would recommend a Squier VMJ/VMP and a Squier Deluxe Jazz V. Unlike the mid '90s squiers, the new ones (especially the VM series) is a great bang for the buck. If you go the 1 bass route, I definitely recommend shopping around for used basses. If you have to buy new, I recommend the Fender MIM Jazz (or P, depending on your tastes). At the right store you might be able to find a used Fender MIA or another decent mid level bass in that range. I would definitely visit as many shops in the area as possible. You never know what gem you will find. Since you are getting the bass for a school band, I recommend dealing local if possible. Guitar shops are not above giving discounts for schools in exchange for a mention of thanks on programs/yearbooks. Not to mention, you'll be supporting a local business, which always looks good.
Best of luck shopping for a bass.
P.S. I recommend going with a Jazz Bass or equivalent. P-Basses are nice, but jazzes have the versatility needed to handle both pep band and jazz band songs. The Jazz neck will also help for any future bassists with smaller hands. There's no guarantee that all of the future bassists will be upright bassists.