Keep in mind that SIAI is headquartered in the San Francisco Bay Area, where the cost of living (and thus salaries in general) tend to be higher. I just did a quick Google search and found that in this area, an entry-level police officer can make six figures plus benefits (and eventually pension), so such incomes aren't really outside the realm of normal possibility.

That being said, I think the offered salary is reasonable, especially given the interesting and important nature of the work being done, and will likely apply for the position.