It wasn't your fault about the horses, but the coach driver is quite adament that you can make your own way to Greyhawk from here.
He seems to have told his story to every one at the 'Coaches Rest' because strangely there doesn't appear to be another Coach going to Greyhawk for a week.
Therefore you decide to fallback to plan B.
You walk into the water front tavern on the docks in Dyvers. Your looking for a ship to drop you off at the city of Greyhawk.