I am currently looking to build a simple purchase order system at our company using SharePoint and wanted to see what the best way possible would be?

Basically I want it so that there is a page where a user submits a request to purchase something (field would include product, vendor, price, use)...and it would get sent to the manager where he/she would either approve/deny it (if approved I want it to list a few choices of payment methods with a drop down box or something)...and then notify the original requester of whether the purchase was OK'd or not...and when the purchase was completed the requester would enter "purchased" and list the total price and possibly attach a file (an image or email as a receipt).