Are the day rates negotiable?

The figure on a card is what that person charges for a standard day of project work. It is a real number, not a starting position, and most people on the roster will tell you the same if you ask.

What does move is the shape of the engagement. Three days a week over four months usually prices differently from five days a week over three weeks, and a fixed-scope block prices differently again. Ask about the shape, not the discount.