The cost doesn't seem to be the issue. The BSA Meteor and the BSA Buccaneer were offered with a rear-sight that could be moved to the end of the cylinder and converted to a peep-sight, and neither rifle carried a premium price for the adaptor. The Sharps Innova and Ace pump-ups were also sold with peep-sights, as were some of the Sussex Armoury springers. This was in the late 70s and 80s. That they were not fitted to more rifles might have something to do with their poorer performance in low light, but more likely the average customer did not understand how they work. The BSA Meteors made for the Army Cadet Force contract ONLY had the rear aperture sight, the barrels were not threaded for the rearsight mounting screws. People who have been in the military will have come across aperture sights, civilians look at them with suspicion - what do you mean 'your eye/brain automatically centres the foresight?' - it seems too simple.
Anyway, if your rifle has a front sight then the Williams sight for airguns is an ideal match and they cost about £40 including post from America - the price of a rubbish scope.
Try googling 'Williams-Diopter-Rear-Sight-for-11mm-Dovetails'