I didn't know that Royal Gun Works ever produced "cap guns".
I have a late 1800's, .380 falling block Pieper, from Royal Gun Works.
Assuming the company didn't change much from the 30 or 40 years earlier when that rifle pictured might have been built, it would have been sold as an "every day" gun for the average working man.
My rifle, in excellent condition, is worth about half as much as the cost of a new, low end Remington or Winchester product.
Little to no collector value unless it was in original/unfired condition (and then still not a great audience - have considered pulling the barrel and turning it into a 38 cal muzzle loader since the ball for a 36 cal cap/ball would patch nicely).
So sorry, can't give you an estimate for that rifle but would suspect that it is probably worth far less than the shop wants for it if the price tag is over 100 bucks.
You can buy an H&R single shot for 100 bucks and in 100 years it might be worth $50 - that's the kind of company Royal was (in it's day).