Vega M GL/GH are a different die from Vega 56/64, if that's what you're implying here. It's smaller (yields decrease geometrically with size) and will be cheaper to produce, and Intel probably gets a reasonably good deal if they buy in bulk.

But yes, even still, Kaby-G is a very expensive part. I've heard ballpark like $500-600 for just the package. You can pretty much buy a whole Ryzen 2500U laptop for just that one item on the BOM. But it's also much faster - roughly 4x as fast as a 2500U.