Buy now script

Hi I am looking for someone who can write me a PHP script that is of similar essence to the "Buy it now" script on eBay. That is to say a script where there are x amount of items, a user clicks a button to purchase via PayPal and once payment is completed the script shows the new total of items available. The script needs to be written in such a way that it can be run multiple times on a webpage with different products, and so that the number of items available can vary for each product. I would also like the number of available items to be displayed as text on the front-end of the script where it is originally displayed. I can provide a picture of how I would like it if this helps, contact me for more information. Although this is generally a small project, there will be opportunity for further developments should I be happy with your work. Any questions please do not hesitate to contact me. Thank you