Prices for a brand new euphonium ranges from around 600 dollars for a cheap student euphonium to around 7000 dollars for a brand new professional grade compensating euphonium.
that totally depends on the player person.... but usually the baritone
The valves on the Euphonium or any brass instrument are used to change the length of tubing, allowing the player to reach various notes. Each valve pressed diverts the air stream through additional tubing, causing the pitch to change. Most Euphoniums have 4 valves but some have only 3, and nearly all current models are piston valved.
The Euphonium is a member of the brass family, and more specifically it is a member of the low brass family.
One could advance from beginner to intermediate in 9 months. Depends upon the desire, practice, study and and advanced help one receives. Some people take longer.
Learn to listen to yourself and others around you when you play. Learn to play in tune and with musical rhythm. That is how you grow and become a better player.