The vast majority of original powder horns were as plain as they could be and still be functional. That means a flat pine (or other softwood) base plug and little or no carving of the throat; just enough work to contain powder and attach a strap. Many times a screw was used to attach a strap to the base plug. A grooved or simply reduced throat is enough to tie a strap around it. The two powder horns shown just below are based on an original southwest Virginia horn and are a little fancier than most with a turned base plug and carved rings at the throat. Even so, it is still much plainer than the carved and engraved horns from the French and Indian War. This horn could also be made with a turned and applied collar instead of the integral rings. The horn would dictate how it is approached.
Please note the raw linen cord used to attach the horn in the photo below. Cord was often found on southern outfits. The outfit show below is much more historically correct for a southern mountain rifle than many of the sophisticated shot pouches and powder horns being recreated today. Most of the original powder horns and shot pouches were very simple affairs, well worn and patched together. You will see horns completely covered in leather to patch a hole or holes rather than just throw it away. Even something as simple as a plain powder horn could not be easily replaced in the southern mountains and was highly valued.
I will make any plain powder horn with a flat base plug and simply carved spout for $75 plus shipping. A horn like #7 with a turned base plug and either carved rings or an applied collar would cost $150 plus shipping