I think my earlier post was insufficiently clear.
3 Guineas (we liked to use those to upset the Spaniards as the gold coins we stole from them were a tad to heavy to use as gold Sovereigns) was not the price of replacement chopper lump barrels in 1895.
It was the extra charge ( in this case on a best BLE by Edwinson Green) for using Whitworth chopper lump barrels on a gun whose base price was £35.0.0d bringing to a total of £38.3s.0d.
Forgive me for using Sterling, but that was how it was priced.
I do not believe a 100 Guinea gun would ever have been re-barrelled by best makers for 3 guineas (unless the customer was a Prince of the Realm, or holding a working gun to their heads, or both).
My WAG is that re barrelling a side by side would be at least 25% to 35% for the current new price of a similar gun.
It is notable however that muzzle loader to pinfire to centre fire to ejector conversions were carried out , which these days would appear absurdly uneconomic.
