What does it cost to use an occupied blue action space, and how many players can use it?

Question

Accepted Answer

Any number of players may place dice on an occupied blue space, paying coins equal to the lowest die value you place; the number and value of dice already there do not matter. Brown spaces take only one die per round.

Marco Polo II: In the Service of the Khan

What does it cost to use an occupied blue action space, and how many players can use it?