How should we handle working with an organization while developing a MVP?

My partner and I are working on a product targeted at organizations. We're planning to approach a few organizations in our area to flesh out our minimum viable product and make sure it solves the problems that we think it solves, but we're not sure how this kind of relationship would work.

What we're building will provide immediate benefits to the organizations we're approaching; but since we're building a product—not a bespoke solution—a client-agency relationship doesn't seem appropriate. Our product would otherwise be billed at $XX,XXX if it were being made under a traditional client-agency relationship. Part of our product's purpose is to put it in reach for organizations that would otherwise find it unaffordable.

How did you handle your early working relationships with your users?