Charging customers on security

Hello,

Our company developers Microsoft Solutions and I am responsible for
leading the security initiative in the corporation.  I have spent a
lot of time and effort on how we should apply security guidance to our
product life cycle, such as adding threat modeling and doing security
review.  But after I have convinced them that security is important,
we brought up a discussion on how we should charge our customers.

Many of you have customer experience.  They want to pay the minimum
and have all the features.  If they can choose not to pay, they won't.
If we tell them threat modeling will add x human-weeks of development
and we have to charge them x thousand dollars more, they won't pay.
Moreover, they expect the system to be secure enough and if there is
anything wrong, they would think that is our fault.

If any of you have any experience on dealing security with customers
and how you would deal with this issue, please throw in two cents. Any
comments or related articles would help too.

Warm Regards.