Custom field in cart based on product

[Richardkl]

I have a custom site.
I have a products
The customer can choose the color and other options
So far so good, but here is where I need custom :
If the customer wants  something like expedited handling , there is a flat fee no matter how many they buy. So I need a drop down that will add a flat fee to the order not by quantity. The fee needs to be by product not global.