Hi Anton,
I have done multiple projects with PHP, mostly for scheduling and logistics. As timetabling was one of my main tasks, I am able to finish your task quickly.
I understand your problem as follows: You have a MySQL database and a wordpress installation. You are using the booking plugin and want a iCalendar (*.ics) file from the booking information in the database. My solution can be either a patch to the booking plugin or a separate plugin - depending on integration you need.
I would suggest that after bidding is completed, we talk via skype and perform a single test booking process, so I can see at which point of the process you would like to have the ics file.
Regards from Berlin,
Guido