I visited Sri Lanka in June end (pretty hot) but almost a very good season to travel across. Starting from Colombo --> Dambulla --> Sigiriya --> Polandua, we reached Trincomalee at the end of our trip. It takes almost 8 hours (a bit more or less) from Colombo, 4 hours from Dambulla. I travelled by public, non-luxury buses (definitely not with chickens) with local people, no AC and it was not horrible. They charged me almost $2 for the trip.