The thing to remember is there is no minimum training requirements. The more prepared you are when you arrive the less you pay for. That means study, take the written tests, purchase the Aviation Instructor's Handbook & Study as many books as you can get your hands on.
The King Videos are over simplified but a good guide to what to expect.
One of my friends did the 15 day thing at ATP in Las Vegas, for MEI first, then CFIA and CFII add ons later. He said you have to have the writtens done as a minimum before showing up.
American Flyers have a 30 day program for CFIA and CFII.
There are also hundreds of small schools that do guaranteed price CFI courses, EX I had a friend go to San Diego for a week and get his CFI done. You gotta surf the web to find current prices though.
Also Research the Checkride Policies in the FSDO regions you look at. Some Regions you go to the FAA for your rides, others you pay an examiner (FAA is free but sometimes harder, sometimes a longer wait fora ride too - depends on the region). So make sure you ask the school you are talking to how it works in their region.
Good Luck