There’s another good post on salary negotiation in an ETG context here: https://www.lesswrong.com/posts/Z6dmoLyfBdmo6HEss/maximizing-your-donations-via-a-job
Back when I was a career coaching, I used to run a popular workshop on salary negotiation for the local job search meetup. It broke down salary negotiation into a set of 6 skills you could practice such as timing your offers, deferring salary negotiation, overcoming objections etc.
The great thing about this was that after the initial presentation, job seekers could practice the skills with each other meaning I wasn’t the bottleneck. Presentation is here: https://www.evernote.com/shard/s8/sh/d45a92cc-a8d0-4b3b-adf5-53b53e1efbc6/a423ecc18c4d0a386b5fe1d2284680f7
I could see a similar idea of a practice group working for EAs.