Rezdent, thank you for that interesting idea. I hadn't thought of that like that yet, but it really does make sense to me now.
However, that would make a brand new iPhone look cheap. 700$ for two years, probably 30 uses per day (if not more...) makes 0,032$ per use. Hairtrimmer: 100$, 1 use per day, 5 years of use 0,054 $ per use.