As a 2nd season OC parent...
My advice echos much of the above... OpenClass is, I think, the right place to start...and more local is better.
If 7th and Spartans are reasonably close, explore them both. Most corps do camps prior to auditions - do those.
Then audition for both, spend as much time as your can with the members and instructors - you would be spending every waking minute of 2 months with these people, find people you like and respect.
There's no real rule-of-thumb for tuition (that I know about).
Also, if you're perc, check out WinterGuard programs. Both my boys started in WGI and I consider it a decent first step towards marching DBC.
The biggest thing is to DO...