Hey Scotters, thanks for all your help. I didn't have time to suss out other drivers so in the end we agreed on the price, albeit one higher than what you have mentioned - US$80 for the whole run. I even threw in some petrol money, sucker that I am :P, but I did it as a goodwill gesture of sorts. Turned out the young driver I was negotiating with was giving the job to a much older man who was pretty nice really. Don't think he gets many jobs. Anyway, the road from Kep/Kampot to Sihanoukville was fine and we had a lovely lunch at a local restaurant right on the seafront where we could see our crabs being fished out of the baskets. Crabs with green peppercorns, yummy!