When choosing a custom there are a few options to consider. think of what type of horn you would like from simple to ornate. Choose a throat style, recessed or not, engrailed or flat, whether or not you want a strap retaining ring. Decide on a design if you desire scrimshaw. If you are a reenactor you have to consider your persona and what that persona would carry. For instance a militiaman would likely not have an ornate map horn, his would be simple with no scrim or maybe his initials crudely inscribed. If you are a hunter I can add a very water tight brass spout with an o ring.
The butt and plug are usually of pine sometimes maple or walnut. i use boxwood and rosewood fiddle pegs or can whittle a plug. The strap adjoins the butt with a forged staple, a knob or a projecting horn lobe.
Size is important too. Often 18th century horns ran over 15", especailly for longhunters and large bore firelock owners. Large horns are often hard to obtain these days due to the recent outbreak of mad cow disease.
Talk to me and we can discuss the options and price. The larger and more ornate obviously would be more expensive.
Remember a horn should be a personal expression of the owner.