Add price comparison from products_opt1 field

On the product page of a webshop (which only displays prices to logged in customers), i need an extra price. The products_price is the price the customer gets and this one is also used to check out. This is however a discounted price. The MSRP (manufacturer's suggested retail price) should also be on the product page. It's (or will be) filled in in the products_opt1. If the products_opt1 has a value, then show it below the customer's price. "Adviesprijs: [products_opt1]" Also add the difference between the price and the msrp. To show the customer how much he/she saved "Uw korting: [products_opt1 - products_price]" The 2 can be on the same line and must be smaller than the actual price.