Congrats!

You may have already lost this battle by allowing it to be an option. If you really didn't want to do it you should have either:

0. Not offered it as an option 1. Priced the option off the table (i.e. 10-100 x the next closest option)

High pricing either makes the customer not consider the option or is enough money to totally make it worth your while.

Also:

1. Why do you not want to do it? 2. Why do they want to do it that way?

What alternatives have you laid on the table that satisfy the majority of their needs within their budgetary constraints?