I did an instructor rating with TVSA and was very happy with their service, knowledge of the industry and value for money. Rating cost $9k and was completed in approx. seven weeks. Their standards are very high and are well known throughout the industry. I think that you would do well to go in to a few schools and talk to their CFI's about the instructor rating that they offer and choose the best one for you. Beware of those who promise you a job. Plenty of Moorabbin schools do. Don't be sucked in.
Best of luck