Earlier this year I bought a rifle from a Forums member. He included an extensive array of bag, capper, powder measures, flask with a set of spigots, and a powder horn.
This was one of those CVA powder horns you can get from Amazon for $9.99 with free shipping, readily identifiable by the huge sow *** sticking outta the wooden plug.
I just wanted a plain and simple, but functional horn for this particular rifle, but just had to do some fixin' on this thing before it could be seen in public. I sawed off the big wooden *** and finished the profile of the plug. I got the brass bushing and plug end from Track of the Wolf and installed it on the reprofiled and refinished wooden plug, and added a rosewood fiddle peg for stopper. Some additional file, sandpaper and steel wool finishing remedied the crude work on the horn, and got rid of the excess shine. I'm still working on a suitable strap, and it no longer looks like a $10 made in India horn. Looks a lot better with the $13+ parts and some hand work.
If you want a quick and cheap functional horn without any fancy design, and don't mind doing a little hand work on it, this is the way to go.
You can always invest more time on work on a more impressive horn as a winter project, meanwhile putting this one to use.