Paypal Website Payment Pro Integration

Hi, I want to integrate Paypal Website Payment pro with my site. I have a custom shopping cart which is all working fine. When user select to pay then I want users to enter their card details on paypal and they are then redirected back to the site and it creates the order in the database. Some users will not come back to the site so it should still create the order in the database. My site is developed in PHP. Let me know how long it will take and how much you will charge. I want to get it done as soon as possible. If you have any question then please ask. Thanks