1.  We’re afraid we won’t get the assignment.  It will go to the cheaper guy.

2.  We’re afraid of being laughed at.  “How much?  For that?  Are you serious?  Wow, you are way out of line here.”

3.  We’re afraid the client will say yes to that big juicy fee, and holy crap we’ll actually have to deliver something that justifies all that money which will be hard because the client will be expecting to be blown away and we might not be able to pull that off which would be hugely humiliating especially if the client wants the money back.