The course is the same for each agency throughout the world. That does not change. As in all cases in all businesses, the price varies by local conditions. Those prices are set completely by the local shop or instructor. The agency is not involved. You can have two shops side by side teaching the same course for the same agency but have different prices, but I would expect that would be unusual because of competition.I'm waiting to take Nitrox until I need it so that it'll be fresh in my mind BTW, does this course cost the same in all DCs? What about in different countries. I can see that OW and AOW prices can differ because different salaries for the instructors but if Nitrox is computer based I would think that it's all the same no matter where you are in the world.
AOW courses can vary dramatically from place to place because of local market conditions but also local dive conditions. It the shop is located where they can walk out the door and do all the dives, that is very different from a place where they have to go out on a boat for all the dives, and extremely different from a place where they have to travel for a day, pay for lodging at night, and do all the dives by boat. Where I live in Colorado, there are no local sites deep enough for the AOW deep dive, so AOWs require a long trip, and most are done on major group trips to exotic locations.