The sentence right after you say the number.
I used to do this all the time.
Quote the fee, then immediately follow with
"...but that includes X, Y, and Z" or "...which I know sounds like a lot, but..."
I was negotiating with myself. Before they even blinked.
Don't: Justify the number before they ask. Do: Say it. Then stop talking. Do: Let them sit with the value you've already established. Do: Treat it like information. The shift?
It's not about confidence tricks or power poses.
It's about this:
If you don't believe the number,
no amount of justification will convince them.
So maybe the real question isn't how to stop flinching.
It's whether you've done the internal work to stop doubting.