Buy now buttons for each post

Hi, we are using the Premiumpress Movipress theme, to use as our online video library. For each video, we also have items for sale. The DVD, Handouts etc. We want to be able to have some fields at the bottom where we would fill out our video post, to have an option to link to these items. They would basically be paypal or amazon links. Then, when the post is live, there will be links below the video, but above the video description. Any ideas of a plugin we can use? Or would this be easy to write something into the site? We want something more automated than just putting links into our post’s text box.

Cheers
Martin