There is no standard. Find attorneys with an hourly rate that looks okay to you and then contact one, two or more until you are satisfied and have the representation that makes the most sense. Until you give a complete and full description of the services you need, no one can possibly estimate how much such an appeal will cost.
Good luck to you.
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Lawyers do not charge hourly fees for social security disability work. They work on contingency. The lawyer received 25% of the retroactive amount with a cap of, at the moment, $5,300. This is due to change 6/22 to $6,000. It is in your best interest, generally, to hire a competent attorney in your area for this type of work.