Discount In Product Options


How to make the options of a product look like discount?

For a product you can have 2 prices the old one and the new one but for options in a product there is only one price.Example i am selling hammers in option i have 1kg hammer,2kg hammer,3kg hammer.When you select eg 2kg hammer i want to show old price 10e discount new price 8e.Any ideas?Sorry for my english