A high fraction. “A dollar’s worth of research” is not a well-defined quantity—that is, the worth of the research produced by a dollar varies a lot depending on whom the dollar is given to. I like to think FHI is good at converting dollars into research. The kind of research I’d prefer to do with unrestricted funds at the moment probably coincides pretty well with what a person with SIAI-typical estimates would prefer, though what can be researched also depends on the capabilities and interests of the research staff one can recruit. (There are various tradeoffs here—e.g. a weaker researcher who has a long record of working in this area or taking a chance with a slighly stronger researcher and risk that she will do irrelevant work? headhunting somebody who is already actively contributing to the area or attempt to involve a new mind who would otherwise not have contributed? etc.)
There are also indirect effects, which might lead to the fraction being larger than one—for example, if discussions, conferences, and various kinds of influence encourage external researchers to enter the field. FHI does some of that, as does the SIAI.
I’ve moved the site to http://www.existential-risk.org/, changed the visuals, and made some other improvements in response to the suggestions that were made here.
There is also a revised version of the new paper (now titled “Existential RIsk Prevention as the Most Important Task for Humanity”): http://www.existential-risk.org/concept.pdf.