Price Matrix - Pricing
You can set the price for an item type to be dependent on the quantity of that type the customer is renting. For instance the 3rd new release might be less than the first 2. And depending on how many days the customer is renting for, the program will use the appropriate column.
There is a matrix tool button so you don't have to fill everything out by hand.
Remember, the matrix is only for overriding normal prices, otherwise you will not need it for simpler pricing.