How close should a dealer be able to estimate registration fees?

I negotiated an out the door price on a beater Civic for my daughter. It was her money so the budget was tight. It looked like it was not going to happen, so I stood up to leave and then the dealer came down $200 to my price. Great, let's write it up.

I will fully admit I did not think twice about the $100 estimated fees listed for registration- I did not think about it on the first car I bought in this state (WA) which was three times the cost and I got $14 back.

So I was pretty pissed to hear that I owed $160 more for the plates. I get it, it's an estimate and I have no recourse and caveat emptor and all that. But 160% off does not seem like a reasonable estimate at all to me. So now we are in over our price because of this low estimate.

My question is it even possible to be off that much in good faith? I figure most of the costs are fixed and only certain taxes are determined later by the state.