Update:
I have bought a C07.621 from MIDO, 21600 low beat, brand new, with nice finish and (finally) blue steel screws! No plastic parts, 80 hours PR.
The price is about $260. The price is pretty high but unfortunately I can't find a better deal.
For those who has a diver with 2836-based movements inside, I suggest that you get C07.121 or C07.621. These two movements are better deals than the modded 2836.
I originally wanted to get a modded 2846 but could not find a decent one. I believe a heavily modded 2846 from a famous Swiss brand would be the best deal, but I simply cannot find it in the market, so I had to go with the second best option.
The movement I just bought is ETA C07.621, also called MIDO C80. It is 2836-2-based. I am happy to post pictures if someone is interested.