Hi - this depends on what you are supposed to deliver. If you need to go to a professional studio, you need to get in touch with them in order to calculate your prices. Otherwise, I suggest you´ll use a per hour basis.
cheers, I offer a price per hour, cause I will need to record with my material from home. I just didn't know what to offer per hour cause checking on internet, I found price ridiculously high ( I know it depends of type of job and professionalism) and others. I bid for a 250 euros per recorded hour. Is that a decent price ?