Like I said previously... I found the cost to be the same among the schools we looked at... at most maybe a $200 a month delta but that's only $2400, not $5000... and the Christian Montessori (no longer open) was actually on the lower end of the price scale.
Also... no one seemed to be telling us that the Montessori system was better... they just explained what their system was... and how it was different (not necessarily superior). As for my wife being an expert... you need more years for that. She just wanted to take the basic classes to understand the philosophy and at the time she was considering going into teaching. I don't even know if there is scientific studies proving one system is better than the other... we just found that the Montessori pedagogy was in line with how we perceived young child education to be. We also liked Reggio Emilia but we didn't see many schools based on that system (coincidentally, the IUSD after-school CDC, according to their materials, is influenced by the Reggio Emilia).
I think the draw for us was there was a system they were using with guidelines by two national associations and accreditation attached. When we looked at something like a Kindercare or Childtime, we weren't really given concrete answers on what type of system they were using and maybe because they were only going up to K... there wasn't a need for it. We had a preference for faith-based pre-schools but those were even more vague about their teaching system (we saw at least 3 different ones).
Since we knew our kids were planning to stay there after K, it was important for us that they had a system in place. In the end, it may just be a wash, but we did find that the methods used were "better" to what we are experiencing now in public school. But like you said, that may to do more with private vs. public than the education system (and the much smaller class sizes).
Anyways, it seems your initial post was based on your own experience which differed greatly from ours and I'm glad you explained it.