This zen cart mod will allow you to enter in your cost for a product as you are entering the product in  your admin area.  You can choose to put in the price, then the markup percent and the pricing field will automatically be updated for you, or you can put the sell price of the product and simply put in your cost in the correct box.

This mod will display a report of all items purchased with the cost and the profit.  It is not a real informative report (not broken down by month or sales, etc) - but serves its purpose.

Written for 1.3.9 ONLY