Home Depot has a cheap Bernzomatic brazing set for about $50-60 that can do small work. Plan on wasting one oxygen bottle getting the hang of it. The MAPP tank lasts a lot longer than the oxygen.

Once you got a rig like that, you'll be able to fab any sort of custom horns you might ever want. At $12 a throw for the pre made ones, that aren't always shaped the way you really want, it doesn't take too many before it pays for itself. I made a half dozen custom horns on the first tank of oxygen and used'em all up already.