Tuba

I have never yet had a student buy their own Tuba.
The really are expensive.
Plus, in an ideal world, you move a student up onto a bigger Tuba as they grow big enough to manage it.
(Until they can manage a full size EEb or BBb)

When it comes to Tubas, the bigger the Tuba, the bigger, richer and warmer the tone.

To give you an idea though, the Yamaha YBB 105 - 3/4 Bb Student Tuba costs $ 4,489

So you can expect to hire a Tuba right through school.
Even now, I play a huge 4/4 BBb Tuba with 4 rotary valves and a forward facing bell, which is loaned to me by the community band I play in. Great bands are always looking for good tuba players, so there's a very good chance you'll never need to buy one.