Best and "free" way to have your essay looked over is at your universities writing center (if you have one). If not, I would go to any English majoring senior or even professor to take some time out of their day (ie schedule an appointment) to dedicate feedback on your essay.
Everyone I ever graduated with either utilized the writing center of the institute, English Professor, or majoring senior students. No one would ever pay a service to do something easily accessible at the university level.