Do recruiters ever provide this information to candidates for a fee? If I was in the market for a job it would be great to pay an experienced recruiter to objectively judge my skills and say how much I should ask.
Why would they charge? They get a placement fee based on a percentage of the starting salary. It's in their interest that the candidate gets the best deal possible.
They get their fee if you are placed. This puts them in a conflict of interest situation where if they can convince you that you are worth less than your true price you will be easier to place. Also the cheaper you are the less work they will have to do to get you placed in a new position.
You really only want advice from someone you are paying and who cannot benefit from under pricing you.