We are a landscape design company have numerous non-inventory items that we use for specific jobs. The costs of the items change from year to year. If we update the item cost and/or clear or leave blank the sales price when entering an estimate the drop down will show the markup but not allow you to select. What would be the best expedient way to update the cost and automatically adjust the sale price with out manually adding calculated sales price? 

By numerous - I mean a zillion items!

I have attached example screen shots 

Thanks!