Are you asking me about how to price a ransom? But first I guess I have to ask, I'm not sure what ransom you're talking about? You have a prisoner in Erasmos, but who'd want him and how much they'd be willing to pay for his release are unknown at this time.
To recap here is brief synopsis (because God knows I can barely keep 24 pages of RPG wankery straight in my head)
Zaral gave you a pouch with 100 gold in it to deliver the news about Zelkor to Petrakos who is a factor with the Kyros' Corsairs Trading Company. He implied that the guards in Odessos might be pliable with bribes, but who knows? Whatever it costs you to get in to lowtown and down to the wharfs, he figured he gave you enough to cover a bribe and still have something left over for your trouble. Secondly, Father Inniros lives in Lowtown (which is east and 300 feet below Hightown) accessed via the great staircase where all of those watchmen were standing around and playing dice when you entered the city. Lastly, Hyginos informs you that Koren Ghul's tower (where all of the fire and explosions and hoopla happened six months ago) it is also somewhere in Lowtown.
Beyond that the world is your oyster - you can go wherever you like and do whatever you like and I have enough stuff prepared that I feel pretty comfortable reacting to whatever happens.
Cheers, and good luck.