Golden Legendaries are 6400 dust

If I craft Golden Rag, that'll cost me 6400 dust.

Then it becomes hall of fame, so I get 6400 dust.
Then I disenchant golden rag, so I get 12,800 dust (total).

The 1,600 dust I lose from not getting the OG full value of Rag is fine. I still paid 6400 dust for 4,800 dust bonus. Which; is 3 free legendaries to craft next expansion.

Doing that with Rag and Sylvanas is 6 free legendaries.