My buddy is interested in selling this but isn’t sure what it’s worth. (If it’s worth anything at all.) Markings on barrel suggest it was built in 2006.
There should be some maker markings on the barrel. You can't really value it without knowing what it is but it does look like a Lyman. If it has a K prefix serial number it is a kit gun. A kit gun will bring less than a factory gun even if done very well. The ornamentation may lessen value of a factory as it is no longer stock but may also attract buyers as this is found on some period rifles.
Black powder is corrosive so how the rifle was maintained is also key to its value. Does the bore & pan area have any corrosion/pitting? You can drop a AA battery down the bore & use the reflection to get a pic but check the breech as well. Check condition of the touch hole, frizzen & frizzen spring too. Set triggers work correctly? All of these things & more affect value.
Make sure the rifle is actually unloaded. A muzzleloader isn't obvious when cleared like a cartridge gun. I bought a plains pistol that was in fact loaded with black powder & ball. You can use the ram rod to help check it.