What should a musician's Performance fee be for prestigious corporate gig?

I don’t know the rates, however you might be able to research them to find out. Go to the website for the function. They should have information listed as possible contacts. Look up prior year’s programs. Use the conference subject or product, etc., being covered as a beginning point, and if program not available. Find someone currently involved, or discover the past performers. Contact them as to what to expect, plus/minus, advantages, would they do it a second time, if able. Ask them for a ‘Ballpark Figure’ or overall rate, of earnings. Remember to ask if travel and accommodations are included in the estimations. Do not ask exact amounts of Professional’s earnings, it’s just not done. If you work with someone within the organization itself, it is acceptable to say that the performer is ‘negotiable’ on payment. “What were the previous or other current Performers offered?” They usually go from there.
If you research this, you should be able to gather info that will help. Good luck.

Your friend needs a talk with a top theatrical agent,

My friend who is a bass player has said the standard rate he gets is about $100 a gig. That’s not a top notch venue of course. But if you use that as a base for the number of performers and maybe double it you would come out around $2,000. So I would consider asking between $2,000 and $3,000.

22 years ago I paid $2500 (I’m pretty sure it was $2500, it’s possible it was just $2200) for the band at my wedding. The piano player played at the ceremony and cocktail hour, and then a full band (I think it was 5 people) for the 3.5ish hour reception Basically, 6 hours of work.

I was going to say a wedding band now is about 5k. I would use that as a starting point.