How might a non-profit public service website be valued?

There are really two common ways to create a valuation:

1. Comparable Company Analysis
2. Discounted Cash Flows

The first utilizes the price of other organizations of similar nature to help you develop a model of your value. The second utilizes a number of metrics to evaluate how much money the organization will continue to make over time and thus determine its value. The last way to evaluate an organization would be to evaluate what all the assets of the organization minus the liabilities are worth.

However, non profits aren't really supposed to generate revenue as their goal, thus the second model is out, and I don't know of many non profits that have been sold, recently, so I think you'd really be looking at one of a few things:

1. The value of whatever assets you can scrounge up to be sold: If the org is only 2 people big than it's hard to sell them as a branch or a subsidiary, so unless you have special contracts that you can sell, I wouldn't include the individuals. The value of the list of individuals in the community. If you can show that such contact lists are evaluated by others at certain market prices, this is a viable mechanism. Or the site itself if it can fitted to generate revenue.
2. Going off the first thought, developing a business model or two that you can explain as potential revenue generators. Chances are, your buyer isn't going to care much about your model and will have their own ideas in mind; however, having a model that both of you can talk about to negotiate around would help your dealings.
3. Finally, being convincing about the amount of effort a potential buyer might need to put into to develop the same user base and level of service. However, this relies on knowing of an interested buyer.

Ultimately, the real asset here seems to be the user base. You might also be able to make a point about ad real estate, but I imagine you'd already know how valuable that is based on the amount of traffic.

a website that provides a free service to a certain community (disability related). [...] run by a charitable foundation [...] there's no charge for the users of the site. [...] How might you arrive at a valuation for the site for purposes of a sale?

Ehmn, "0"?

I don't get it -- if the site

• was created by a charitable foundation (which is probably tax extempt)
• made available for the community as a free service
• all users signed up under these terms (so you can't start exploiting their information aggressively for advertisement / cross-marketing purposes fx)

.. then what do you plan to sell? And moreover, if the owner is a non-profit foundation, why should it even "sell" at all?

The infrastructure code could be worth the billable hours it would take to re-create it from scratch. I mean, the basic code that makes up the website (without any data) could perhaps be sold to someone looking to make a similar site. But on the other hand, perhaps you couldn't even sell the code, because of "not invented here" syndrome.

I would say the website is worth the replacement cost for the code, maybe.