Add integral shopping basket to existing website

I have another developer coding the webpage at the moment which will be finished in a couple of days. I then need someone to write an internal shopping basket, so that a customer can Add To Basket without leaving the site. When they have selected their products, there will be a form where they select their delivery date. This information is then passed to Paypal and all items and delivery date passed to Paypal, so that my client can see the details. The customer then returns to the original website once checkout is complete with a thank you message appearing. My client then receives an email letting them know about the order with the order details. When a customer clicks on VIEW BASKET, a slick popup will appear in the middle of the screen, showing the items they have added and the total price. If they click on CHECKOUT on this popup, they will need to select their delivery day and then date from drop downs. They can't check out without selecting this date. This date selection is already being done by the current developer on another area of the site in Javascript, so you can use his code for this part. I don't mind how this is done (PHP/mySQL etc) but it must work properly and be an easy experience for the customer buying. No time wasters please. If you don't do this exactly as described and as the client wants it, the job will be given to someone else and you won't be paid. This needs to be done by 21st March. If you are interested, I can email you the current link where the website is being developed.