Help with a custom Field

[hotrod]

Version 2.0.22a

I run a Truck Parts Store..
We have core charges on some parts which are refunded once the core is returned.
Right now I am using a string to say Price includes core charge of $200.00

I really would like to set this up as an attribute that is automatically selected and that I can refund in the invoice once the refund has been given.

I was able to do it in a 1.5 version but cant figure out the setting in 2.0

Rod