Just an aside, this is the type of pricing thread we welcome here on Paint Talk. A “how to price” thread is infinitely more valuable (and totally within the rules) than a thread where someone is just asking how much they should charge.
And to add to what Kevyn wrote, don’t forget the masking or removal of door hardware, whether it be man doors or cabinet doors. Then, it all needs to go back. Hinges can be especially problematic so make sure to label each each one as well as the spot on the doors where they came from. It’s amazing how a group of apparently identical hinges will vary enough to make reinstalling any door a royal PITA if they don’t go back exactly where they were. And if the customer ever wanted all new hinges or pulls, well, I always did those on an hourly basis because I never knew what I might be getting into. Or, if it was a really challenging change over situation, I would recommend they have a cabinet guy do the new install for them so I could stay comfortably in my lane.This is a pretty loaded question. Have you done many kitchens? Firstly and most importantly you need to know how much your time is worth. Secondly, you need to know how long it takes to perform tasks. Keep a log and then you can make up any formula you want. There is no set in stone way.
However a per door charge is the easiest way. (imo). I also charge for end panels, wine racks, crown moulding and light rail. Will you have to repaint walls after? In my experience a good starting point is about 2 hrs labour per door, including its box. Times that by your hourly rate and voila. However sometimes people only want the doors done. Sometimes you have to drill holes. Sometimes you have to fill old holes. Everything should have a time allotment and you need to make up a price list. EG. How long to take a door down? How long to install a door? Keep it in your files for proper pricing for every situation.
Every kitchen is different.