Assuming you are fresh from your commercial, you shouldn't be spending more than 8 hours in a plane for your CFI. You already know the maneuvers, you just need to practice them in the right seat (it's really no that different). The only thing new you are learning is teaching and that can be done on the ground. As stated before, CFI is 90% self study.
Look at a few free private pilot syllabuses online and then make your own. It will take a lot of work, but designing your own syllabus is a great way to learn how to be a good instructor. Once you have done that, then make your own syllabus for your CFI training. Try to find a student pilot and practice explaining maneuvers to the on the ground. Once you are comfortable with all that, then you are ready to get into a plane. I spent $4,000 (2008) for CFI, CFI-I, and MEI.