I agree that all of the on-the-ground learning, including sims and radio practice, will save you $ time in the air.
In this case I don't recommend going the P2P route. All of your training is in prep for checkrides, and the more often you're in the cockpit, the fewer total hours you will need to pay for to be ready for your checkrides.
That means if you go the "buddy CFI" route, you'll probably take longer and maybe even pay more in the long run than going through a flight school. I'm sure there does exist a CFI somewhere in your area who's independent, available, and reliable, but he/she will be pretty hard to find.