You can play around with this tool to get a quick idea of how food & housing costs vary:
Generally speaking I think you are right that most cluster in a tight range. But unsurprisingly, some NYC colleges, say, are significantly above $20K/year, and also a few other privates.
Then there are actually quite a few below $15K, some even below $10K. BYU is famously cheap–but of course kinda a niche school. Purdue has been keeping costs frozen, a lot of schools in the Midwest, South, or Southwest are less expensive . . . .
Looking at that list, I was just reminded Cornell College (Iowa) actually has a low list price for a private, and then they have merit that can bring that even lower. Cool block structure (one class at a time) which some find very appealing.
Lots more prominent Midwestern SLACs are around the $12-13K mark–not a huge deal but it can add up.
Like, another poster mentioned Kalamazoo. Really cool SLAC in many ways, in a nice decent-sized college town, and although not quite automatic it again has a merit scale based on GPA:
Full cost of attendance only starts at like $79K (this is everything including books and travel and such), quite a bit less than usual private COA in more expensive markets. Then a top award of like $44K would bring that down to $35K. Not bad!