Do they expect the most talented to be more likely to accept a lower salary for a good cause?

Yes. Any one with the necessary mindset of thinking that AI is the most important issue in the world will accept a lower salary than what's possible in the market elsewhere.

I don't know whether MIRI has an interest in hiring people who don't have that moral framework.

Two notes: First, the term "genius" is difficult to define. Someone may be a "genius" at understanding the sociology of sub-Saharan African tribes, but this skill will obviously command a much lower market value compared to someone who is a "genius" as a chief executive officer of a large company. A more precise definition of genius will narrow the range of costs per year.

Second, and related to the first, MIRI is (to the extent of my knowledge) currently focusing on mathematics and formal logic research rather than programming. This makes recruiting a team of "geniuses" much cheaper. While skilled mathematicians can attract quite strong salaries, highly skilled programmers can demand significantly more. It seems the most common competing job for MIRI's researchers would be that of a mathematics professor (which have a median salary ~88,000$). Based on this, MIRI could likely hire high quality mathematicians while offering them relatively competitive salaries.

Highly variable with skills, experience, and how badly they want the job. I bet there are some brilliant adjunct professors out there effectively making minimum wage because they really wanted to be professors. OTOH, I bet that google programmer isn't just being paid for talent, but specific skills and experience.

From some WSJ article:

The setting of Einstein's initial salary at Princeton illustrates his humility and attitude toward wealth. According to "Albert Einstein: Creator & Rebel" by Banesh Hoffmann, (1972), the 1932 negotiations went as follows: "[Abraham] Flexner invited [Einstein] to name his own salary. A few days later Einstein wrote to suggest what, in view of his needs and . . . fame, he thought was a reasonable figure. Flexner was dismayed. . . . He could not possibly recruit outstanding American scholars at such a salary. . . . To Flexner, though perhaps not to Einstein, it was unthinkable [that other scholars' salaries would exceed Einstein's.] This being explained, Einstein reluctantly consented to a much higher figure, and he left the detailed negotiations to his wife."

The reasonable figure that Einstein suggested was the modest sum of $3,000 [about $46,800 in today's dollars]. Flexner upped it to $10,000 and offered Einstein an annual pension of $7,500, which he refused as "too generous," so it was reduced to $6,000. When the Institute hired a mathematician at an annual salary of $15,000, with an annual pension of $8,000, Einstein's compensation was increased to those amounts.

Many such geniuses (top intellectual performers in fields where they can out-perform the median by several orders of magnitude) choose their work not just on the basis of payment, but what they work on, where, how, and with whom (preferring the company of other top performers).

If MIRI were to compete with Google at hiring programmers, I expect money be important but not overwhelmingly so. Google let you work with many other top people in your field, develop and use cool new tech, have big resources for your projects, and provides many non-monetary workplace benefits. MIRI lets you contribute to existential risk reduction, work with rationalists, etc.

Eliezer once tried to auction a day of his time but I can't find it on ebay by Googling.

On an unrelated note, the top Google result for "eliezer yudkowsky " (note the space) is "eliezer yudkowsky okcupid". "eliezer yudkowsky harry potter" is ninth, while HPMOR, LessWrong, CFAR and MIRI don't make the top ten.