The current filing fee for an I-765 is $ 380. But we would need to know what is the basis for your employment authorization to determine whether this fee or some other might be required. For example, persons who filed for adjustment of status after July 30, 2007 may not be required to pay for extensions. If your employment authorization is based on some other status, like an H-1B or other nonimmigrant status, the fees are different.
There is not enough information here to answer your question. Filing fees are posted on the USCIS website, and would depend on how you qualify for the EAD and, if you qualify for it based on adjustment of status, when the adjustment of status was filed.
You should retain an experienced immigration lawyer to review all the facts and advise you accordingly.
J Charles Ferrari
Eng & Nishimura
The statement above is general in nature, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship.