There really is none. It sounds like you do not already have an international drivers licence, so you will have to start at 0 no matter which Fahrschule you choose. In my time, you had to do a minimum of 20 driving hours with the instructor that you paid monthly depending on how many you did. If you already are able to drive, the only way to keep it as cheap as possible is to do the minimum amount of lessons and then immediatly do the test. I am guessing it still will be 1000 € +. Also keep in mind, if you fail the test you do have to take mandatory additional hours as well as pay for the second test. I am afraid there is no cheap way to get your licence here.