I made myself a diopter correction eyepiece for my Nikon FM/FE using very minimum tools that I have. Next time I may try to use hole saw to make a perfectly round lens.
Standard eyepiece from Aliexpress : $20 for two
Reading glasses from Home Depot : $4.50
The lens from the reading glass is thicker than the original that came with the eyepiece so I can't reuse the locking ring. I will just glue it with clear glue.
Total cost should be less than $25 for two eyepieces but I ruined the other lens with careless mistake.