Any firearm is worth what someone else is willing to pay for it. I would say that $500 is a reasonable asking price for an 1894 Marlin, whether the caliber is 44 mag, 45 Colt, or 357 Mag. Because the rifle is coated with cerakote doesn't really make it worth more, unless that is something you are looking for. Customizing a gun, or an automobile, always seems to make the owner think it's worth more, but once you customize it, it is no longer original and any possible antique value as the item ages will be lost. So, there are two ways of looking at custom work, in one person's eyes the value is increased in another person's eyes the value is decreased. I own two Marlin's in 44 Mag, and I would probably sell one for $500 if I got an offer, but it all depends on the circumstances. I own 14 lever action rifles, most of them are Marlins...