They have some extras built on top of it, but imo yeah mostly marketing. In general no one knows how their arrangement with Microsoft works, would be nice to hear the details.
Prices are here:
https://azure.microsoft.com/en-us/pricing/details/cognitive-...
Little known fact: if you buy anything on Amazon, DuckDuckGo gets to know exactly (the precise item) you bought as part of the Amazon affiliate program.
This isn't specific to DuckDuckGo in any way whatsoever. This happens for ANY affiliate. I've used the Amazon affiliate program, and every month I would get reports of the exact items people were purchasing. I couldn't link those purchases to any particular individual, mind you, but I could see exact items.