I want to add a attribute to some of my products with a special price.

It has a administration price of €3,50.
The price is a % of the product price, but it can't be lower then €35,00

Sample:
Product price €400,00
Administration = €3,50
special price = (400*0,10 = ) €40,00

So if they want the attribute it cost 43,50 (40,00 + 3,50)

Sample 2:
Product price €200,00
Administration = €3,50
special = (200*0,10 = ) €20,00 but 20 is lower then 35 so it is 35

So if they want the atribute should be 38,50 (35,00 + 3,50)