I have added to umbraco a new section and called it 'eCommerce' where content manager can add all company products, then in the Content section they create the page and link it with the product node from the eCommerce section.
All the product details are created in the eCommerce section and saved in a table other than cmsContentXml table. Now, how can ExamineIndixing index those information and display the right link for the page that should display such information?
Here's some documentation and a sample project on how to index custom data: http://examine.codeplex.com/wikipage?title=Custom%20Indexing&referringTitle=Documentation
I'm not quite sure why you would want to write your own custom commerce solution on top of Umbraco though, as there are already 3 fully featured commerce packages available for a more than fair price (uWebshop, Tea Commerce and uCommerce: http://our.umbraco.org/search?q=commerce&content=project).