Mostly, people don't think of Craig's List for brass instruments, but that's a mistake. Stuff shows up there fairly frequently, and often at surprisingly low prices. For example, I've been looking for a really affordable Euphonium for a couple of years, and have seen hundreds of them on eBay, but I couldn't see them or try them. On CL, that's no problem. It works best in larger cities, of course.

I finally found the perfect horn, a recent Blessing three valve Euph, with case and in excellent condition for just $125. It took two years, but in that time, in the twin cities of MN, I saw listings for many dozens of euphs and tubas of all brands. Here are some tips for finding interesting possibilities:

Search broadly. The Euphonium I bought was listed as a baritone. I've seen others listed as brass horns, band instruments, and tubas.

Search daily. If an instrument is listed at a low price, it will be gone tomorrow.

Act quickly. Reply to the ad immediately, and go see it at the earliest possible time. He who hesitates won't be the buyer. If the price is really low, the eBay sellers will snatch it up if you don't act fast.

Watch for stolen horns. Ask the seller for history and reason for selling. If the story doesn't make sense, be wary. If the owner plays, ask him or her to demo the horn for you. Can't play it? No reasonable story? Skip it.

Meet in a public place, like a community center or Starbucks. No parking lots.

If it's a lot of money, transact the sale at a branch of your bank. Don't bring cash. Be safe. If it's just a couple of hundred bucks, though, no worries if the story seems OK.

Play the thing. If you're not a player, get the owner to demo it. Pull slides. Check valve action. All that stuff.

Good luck. You could find a real prize at a great price. I did.