I guess I'd ask a slightly different question. Why do you want the cheapest possible PPL? One thing I can say for sure is that if you think learning to fly is expensive, wait until you actually start flying afterwards.
If you just want to get a PPL for the experience of it and so you can feel good about having achieved something substantial (and absolutely nothing wrong with that), then sure, do it the cheapest way you can, frame the certificate, and get on with the rest of your life.
But if you're doing it so you can fly afterwards too, then you need to think about the bigger picture, in particular how you are going to stay current and safe. That too will cost money. Flying a handful of times a year is not safe, unless you do it with an instructor every time.