I'm leasing a trumpet from St. John's Music right now -
www.stjohnsmusic.com/ - they carry pretty much the full range of Yamahas, from student models up to Xenos, so if you're looking for other models you might want to look elsewhere. I'm just leasing temporarily, as I had about 3 hours notice to find a trumpet last year...I plan on finding a good used trumpet eventually, or possibly finding a rent- or lease- to own Xeno or Strad or something along those lines.
Your best bet might be to ask music teachers and ~pro trumpet players where they got theirs, if they have friends selling trumpets, if they've been ripped off or pleasantly surprised by stores or models in the past, etc., as that's probably the best (maybe the only) way to find good used instruments unless you get very lucky. A few friends have scored great trumpets that way, in excellent condition and for a fraction of retail price.
Long & McQuade only carries beginner models so that rich parents can buy instruments for their kids to try out or start taking lessons when they're really young. Cosmo had a crummy selection of useds when I visited, but instead of browsing the new trumpets, I was more interested in trying out a piccolo trumpet
. I'm under the impression that retail prices for new trumpets are pretty much similar at any store, but you'd have to compare to be sure. Ask any music teachers you know if they get discounts at instrument stores and ask them to buy it for you. Theoretically, eBay or American dealers might be cheaper in some cases, but there's that added risk and you don't get to try it out before you buy. Remember to factor in the cost of a hard case or a warranty, or stuff like that.
I don't know how much you play, but if you intend for this to be the trumpet you play for decades, spend a little extra if you need to, get the best trumpet you can afford, and you won't regret it. The good thing about trumpets is that the highest-end models are arguably the cheapest compared to any other instrument. Better to be in debt when you're young than when you're about to retire.