Hi, I would like to offer you my expertise in digitla, analog electronics, Hardware and PCB design and embeded firmware and software development.
You have interesting project and I can help you with it.
I would suggest developing embedded linux based system upon wich I would deveop addition hardware - locking mechanism for door, credit card reader system, display, and item (food) detection system. This will all be supported with software I would provide along which would provide additional GUI and payment gateway.
Lock mechanisam can be based on magnetic lock, and food detection system (detecting which food is taken) can be based on RFID reader, every item can have small RFID tag, and when system is not reading one item in particular that means that item is taken by user and should be charged.
I woudl offer you hardware + software development and prototype assembly which I can deliver to you.
Feel free to contact me over chat.
Vladimir.