OK, so looking at the DMG (finally). It looks like the ranges look about right.
A "realistic" price would be 10 gp for the pistol, 20 gp for the musket.
A heavy musket i'd put at 50 gp, 2d8 piercing damage, 20 lb, Ammunition (50 / 150), loading, two-handed, heavy.
Ammunition should be 1 sp...