Regardless of which method you use for joining tubes (tig or fillet braze) the biggest obstacle you'll likely face is fitting and holding tubes to produce a strong and straight frame.
For a first timer you'll spend a lot of time mitering tubes, and then devise some way to hold the tubes for welding. I can't imagine doing this in a classroom environment unless you can leave you workpiece "set-up" while you go home for the night. It's a PITA to teardown, clean up, and set up at the begining of the next class. IDK, maybe your class setup will accomodate this.
Local supplies, if there are any, will most likely be expensive. If you source straight gauge 4130 from someone like MetalSupermarkets, or Aircraft Spruce, it is considerably less than bike specific tubes from someone like Nova or Henry James. All the sources mentioned have outlets in CA, just not close to you.