Depends on the person you are hiring for doing it. If you do it from a reputed CA it could be around 5,000/- plus Service Tax.
However same thing would be done by some other person for Rs. 2,000/-.
New Registration under GST has not been started yet, Once registration process starts fees can be confirm, till date there is no such fees for Registration, only professional fees to be paid to the person you hire for getting your GST registration.