Alterations to Booking process and other pages

I have an on-line accommodation reservations system. I need the booking process to add "optional" and "mandatory" addtional charges (where they exist) to the booking process, then these charges must be calculated into the remainder of the booking process and added to the db and then extracted and correctly calculated and placed into existing "invoice" and "contract" pdf files (6 altogther).The pdf files are already created but need some adjustments made and formatting corrected. The booking processes are all in place so there is not mcuh prgramming to do as far as that is concerend. Just the addtions and some of that is also in palce but will ened to be tweaked.. There are a few other small issues in other files that need attending to such as dynamically showing some input fields if a certain radio button is selected. There are also some issues when a user clicks "back" during a booking process. Establishment Id's are getting lost somewhere and not all the time so this will need to be tested. There are some things that need to be taken into account and I will discuss this in pm's with the worker. Mainly around "What details get shown to user if the establishment is sold on a 'per-room' basis or 'per unit' basis. If on a per room basis then the user can select a room BUT if on a 'per unit basis' then user does NOT select a room however the unit paramaters (unit name) needs to be carried through to the rest of the booking processes. I will explain this in detail when we get going. See document attached for web address and login codes to test what you will be required to work on.... I will pay when the whole project is finished... no progress payments so please dont respond if you want payments before the project is 100% complete...