Billing model for WPMS's for nonprofits w/ local branches

I'm trying to think through this:

The idea is to partner with the central office of a nonprofit that has many small local branches that each kind of run their own show. Currently the branches each work to develop their own web solution, whereas it would be much more efficient for them to all use the same template with minor customizations (i.e. a multisite network)

So the question is:
-- Do I sell a product to the central office, which it in turn provides as free product to all its branches (plus hourly support)?
-- Or do I create the product and sell it myself to the individual branches, with paid help from the central office?

(And of course, I'm open to general advice on the subject.)

(And of course, if I should offer both options, I'd appreciate any help fleshing them each out from a billing standpoint.)