Currently the fees for an L-1A or L-1B is $325 plus $500 Fraud Detection fee plus an additional optional $1225 for Premium Processing Fee. The visa fee itself when going to the consulate will be separate. In terms of legal fees, they do vary and most attorneys would need additional facts before providing a quotation for services. You should consult with an attorney to get a better sense of the fees involved with your fact pattern.
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Your situation is fact specific. The USCIS filing fees are fixed fir the various petitions for you and your family members. However, need more information on the other issues. Are you referring to setting up the business? Labor? Building and other costs? These costs will vary by location Attorney fees will vary too. Perhaps you should consult an immigration attorney in the OKC area. Good luck.
There are no set attorneys fees, you will have to find the best lawyer to do the job, and within your budget. If the sole purpose of the business you are opening is to be able to do an L1A, you should be prepared for disappointment, because this is intended for businesses that are opened to make a profit, and only incidentally require an executive or manager to come to the U.S.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.