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I'm a senior in high school, and I think I want to pursue a degree in Music education. I play brass, mostly Trombone (for Jazz) and French Horn (but started as trumpet, you know the story), and I have played tuba in a duet with a buddy. I really loved playing tuba for the 3 weeks (?) that I had one, and I want to/need to learn some more. Any tips including where to rent a horn, or what kind of horn I should buy (preferably not, I already need to buy a pro level French horn) any tips are really useful. I'm moving the Yakima, WA area soon if that help or if there is anyone there that is in the know.

Finding a rental will be nearly impossible. Finding an easy-blowing, serviceable, $500 BBb, perhaps even with 4 valves, shouldn't be too difficult. Makes and models from the last 50 years are too numerous to list. Try before you buy, and have a good tech check it out where possible.

I love playing tuba and I studied music ed. too. I would urge anybody in a position like you describe to concentrate on the horns you already know best (reason enough) and then to be preoccupied with learning whatever you reckon to be the most lucrative over many years. Then look for recordings featuring tuba in popular music, and size it up against other types of instruments. Decide for yourself, but at least see how much "market" there is for playing.