What is the highest post-doctoral salary one should ask for (immunology) I know the average salary is generally 45K USD for science post-docs. However, I received an email from a team of researchers who I had an excellent interview with and basically asked, "How much do you want?"

I have no idea what is the maximum amount of money I should ask for without being insulting. I'll be honest, although I don't do science for the money, this would definitely help make a decision for this particular posting.
Postdoc salaries as high as 60K are not unheard of, especially if the cost of living is high and/or you have children. I believe some very competitive "independent postdoc" positions can even reach as high as 70K. However, these salaries may not increase annually, while typically lower salaries do increase annually.

BTW I believe the average 1st year postdoc salary is under 40K (and so is the NIH postdoc salary guideline).