You'll definately see Nitrox classes for different prices at different shops. But different shops also include different stuff. They may or may not include the books, DVD or VHS video, rental/tanks-air-fills for class, or actual check out dives or trip/dive costs.
My LDS charges $120 + $45 for books, but includes the rental tanks and nitrox fills and the check out dives at any of their quarry trips or ocean trips. But they put it on sale at Christmas for $69-$79 plus books ($40) with the same included.
The $189 + $75 for books does seem a little high compared to other prices I've seen on here. There was a thread sometime last year about what Nitrox classes cost. I've never seen the PADI books cost $75 bucks though. Thats very high. Maybe that cost included the video?
There was a thread on here last year where a lot of people were discussing price and what came with it for Nitrox in their locations.