CFI-intial
You don't necessarily have to write all of your own lesson plans. You'll need to know the mechanics of writing one (how to write one with the appropriate bullet points) but you can get away with a commercially produced lesson plan book. I know because I did. Just try to make sure the lessons are detailed enough to cover the areas you would include if you were writing it yourself.
You can save some money and go to your local flight school for this rating. Just make sure the instructor has recently trained a CFI and has a good pass rate. He'll prep you well enough. The main thing: study harder than you've ever studied before. This was up there as one of the top two hardest tests ever taken, and I have a masters degree (just for perspective).