I did the analysis as well, calculated everything and ended up paying 500 bucks for an external service. Everything else would have cost roughly the same (with

I did the analysis as well, calculated everything and ended up paying 500 bucks for an external service. Everything else would have cost roughly the same (with buying a good and used slide scanner and selling it afterwards) plus the countless hours for loading and unloading the scanner and retouching, etc. Just use an external service - if he doesn't trust "some online service", I found a lot of small, family-owned businesses in drivable range to go to. They're usually more expensive, but you know where to knock if something goes wrong.