Replacement electric razor foil
Most replacements are almost the price of a whole new shaver. And I haven't even found a replacement for my modified, ancient Braun system 123.
After the shaver died I resurrected it and made it solar powered by tearing out the charge circuitry and batteries and replacing them with two batteries and a diode that plugs into a small solar panel from a garden light. This worked perfectly for years until the foil wore through last week.