Hi Rob,
One of the reasons that info. is a bit thin or vague, is that timetables, services and prices change quite a bit over time at very short or no notice. It's difficult to keep up to date!
The ferry service was suspended due to the storms in the wet season and a lack of passengers. We do expect it to start again soon for the tourist season. The last price was $25 US.
At the moment there's only one regular bus service from Koh Kong, which departs from the town (20 mins by moto from the border) at around 8 a.m. Priced at $14 US at the moment and takes around 5 hours.
With the road in good shape and bridges all complete, we expect more buses to ply this route in the near future.
At other times of the day, there are taxi & mini-bus cowboys that can get you here at a price.
Drop me a line closer to your arrival and I'll get you the most up to date info.
Cheers
Mick
ANA travel