less of inicial price

How can I do for put an option in a product for less the price?
For example I have “free shipping” but in thru goes included, so I want when select the “Local pickup” option less -80$.
I have put “Local pickup” option less -80$ and works with others select options but when you don’t select a plus options and only “Local pickup -80$” don’t lees from the inicial price

Thanks

Alfonso