So far I have only seen a bounty collector, in Samarach. Is there one in Sword Coast? Although selling to bounty collector yields more gold, it's inconvenient to go to Samarach to sell bounties.

There's Kwesi in Samargol, and Nil in the Lantanese Lumber Camp. Nil is only available after completing 'Local Troubles' in the logging camp.

I see. Is it still inevitable to spend 2000 gold in order to teleport to Lantanese Lumber Camp?

You can use the portal in the merchant headquarters for free.

Currently the portal keeper is charging me 2000 gold each time.

Hmm! Maybe I'm remembering it wrong then...

I just checked, and it's free to any trading posts you own, so that must be why it's costing you.

I see. Thank you.

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Now the portal keeper no longer charges me when I want to teleport to Lantanese Lumber Camp. Maybe that's because I had took over the control of the headquarter after Sa'Sani left.

Yes and no.
After Sa'sani left, is supposed that you will follow her, and as is a trouble time, the gnome give you free access to the portal.

I didn't notice the gnome say so. And there were three options on who operates the business: I, majordomo, or Khelgar. And I chose that I do it.