Never claimed to be an expert!
But I think you are all getting a bit hung up on the techno terminology and there in no mystery or mystique to this stuff. Just coming up with enough cash and the right dealer to set you up properly and away you go.
I've seen two types of sears sold. DIAS by themselves at a cost of about $4000 and completed machine-guns with DIAS installed selling for $5500 to $6000. The sear is still the registered NFA item. What's the difference? It's still a sear gun whether complete or just a part. Seen receivers sold the same way, as a part or completed gun. Market has gone so nuts that there is no longer a economic distinction between the two (receiver or sear). Both have become equally as expensive.
Uzi machine-guns have either registered bolts or receivers and was just generalizing the different types of total possibilities.
When you are spending $1000 a year to maintain a manufacturers license in order to own one gun. I think anyone would consider that as expensive.