Virtuemart shipping per item fee calculator

We have a client using virtuemart. When people buy their first item we want it to show $7.50 as the shipping cost. If they purchase a second item we want it to show $15.00. If they purchase a third or more items, we want shipping to remain at a maximum of $15.00. We want this to show in the checkout as the shipping cost, rather than be included in the cost of the product.