Nagas?

How much per hour is it at nagas?

 

It depends on whether:
1. you're solo grinding or doing special deals
2. your RNG
3. how many hours you grind before the two daily resets (special deals)
4. and if you use the item collection increase scroll (from 90 Day value pack in pearl shop)

Nagas is very good (or the best as far as I know) for black stones, and if you grind at least 1-2 hours before reset you'll be able to maximise silver gain from the server buying out your seraps (for special deals only).

Solo grinding wise, seraps are pretty much trash. Nobody buys them off the marketplace. I sold mine to NPCs.
Black stones are in high demand near/on FS weekend, so you will be able to list them at max price and get them sold. Especially the armor stones.