Change quantity of items and recalculate price

Okay so I have this problem on a site im working om.. The site is very small.. it's made for a small business so they can send out an offer on their products - you start by selecting the main product. then you have to select some accessories. some of them are mandatory to select, and some are not. When you have selcted all you need, it is then all send by POST to a page called pdf. (in the future this there's gonna be a button to convert the page to a pdf file.) Now on this page all you have selected is shown, and there total price is added up and a total sum price is displayed. a price for consumers and one for retailers. And here's what i need done to the site. I need a function where you are able to change the quantity of the items selected shown on the "pdf" page and then the price is recalculated, with the use of an "update price" button, automatic or somthing like that - also there has to be a field where you can type a percentage and then that is subtracted from the total sum price as a discount. I have the site ready and the database for it which I will send to whoever gets the job. i have attached 3 screendumps of the site so far, so you can see the 3 steps there is.