Well, your spare time is by definition worth $0. Nobody would otherwise be working during the time they're looking for keys. I think it's important to do this type of calculation for things at work or for side projects but you know how you can not lose your keys and not pay several hundred dollars for a fob? Put them in the same place every time.

Also the fact that you can buy something nearly identical for $1.40 pretty quickly rules out paying several hundred dollars for it.