Six books at $19.99 for Kingmaker, also available at $13.99 as PDFs.
Also, it's worth noting that those are an Adventure Path (modules), and not necessarily part of the setting as such. $120 is probably not too bad for a full campaign good for at least a year's gaming...
But Pathfinder can certainly get horribly expensive if you try to get everything.
Although a lot of setting detail turns up in the adventure paths and other modules, I think he meant the actual setting splats. I.e., the Pathfinder Chronicles and Pathfinder Companion series, or whatever they've been renamed to. I've spent way more than $120 on Pathfinder setting material, and that's not counting the adventure paths. Off the top of my head, I've got: the Pathfinder setting book ($50), the Guide to Korvasa, Classic Monsters Revisited, The Guide to Darkmoon Vale, The Guide to Absalom, Guide to Katapesh, the Great Beyond, Princes of Darkness, Seekers of Secrets, Cities of Golarion, Classic Horrors Revisited, Faction Guide, Heart of the Jungle, and City of Strangers (all... what, $18-20 or so?) and the Osirion book, the Taldor book, the Qadira book, the Sargava book, the Orcs book, and the Cheliax book (all $10, I think.)
Not even counting the adventures, I've spent at least $350 on Pathfinder setting material, and I've only picked up about half of what's available. So yeah, being a collector/completionist over Golarion might possibly be the most expensive setting endeavor you can do. They're in their seventh adventure path, with six adventures each (at $20 each) and there's gotta be nearly fifty unlinked modules available too (at #13/pop). Even to date, you could easily have spent $1,000 on Golarion material, and there's more coming all the time.
