Actually, something like a Brown Bess, used by both sides in the Revolutionary War, can be had for less than most folks think. A good, though not top condition one will run $2500-3500. Better ones can go higher, of course. And a good original is a guaranteed investment, but caution is needed in the antique market whether the area is guns or furniture or coins.
Replicas of both the Pattern 1756 Brown Bess and the French Model 1763 (supplied to the colonists by the French) have been made and in all respects but age (and price) are the same as those used in the War of Independence.
Unless you and your father have money and are desirous of obtaining original guns, a replica might fill the need.
I suggest a Google search on "Brown Bess" and "Charleville." You will be able to see prices for originals as well as prices and sources for replicas.
While the Pennsylvania (Kentucky) rifle captures the imagination of many Americans, it was slow to load and had no bayonet, so it was not much used in the war. Carried by men from the wild frontier areas, like Western PA, it inspired some fear in British officers for its accuracy in long range sniping, but the war was won by the Americans adopting the European style of fighting and the muskets that went with it, not by frontiersmen with long rifles.
Jim