Automatically generate selling price depending on purchase price.

I realized that your website does not have a option to fix my margin for sale. eg. If I have purchased multiple products at X,Y & Z prices, there should be a option to fix my Profit of margin automatically at a desired percentage. This will reduce the amount of "manual" errors that one could create. Once the person has decided on the margin for a particular product, it should also automatically update the sale price incase there is a fluctuation in purchase price. This should be available also in bulk import as I stock 50-100 products from every company I work with. Single and manual changes might take forever and result in occasional losses.