[Kyle]

If the site is actually making money, then you should expect at least 10x monthly income. There are plenty of available buyers that will pay 10x - 12x for a solid earner. If it's a good one keyword .com name that certainly would add some value too.

edit: It really doesn't matter if the majority of $ comes from one keyword, that is a risk the buyer will take and all part of the game. No rankings are ever guaranteed and like Jeremy points out in his blog taking risks in business (and failing sometimes) is necessary for success.