Have just got back from Sri Lanka which was a fantastic experience except for the first week which was ruined by having a driver/guide. Please let me recommend NOT to get a guide, and if you get a driver, meet them before you agree terms.. We got a driver and "guide" after saying we wanted only a driver as we knew where we wanted to go. I am now sure the "guide" we had had recommended his services pretending to be a traveller on this forum, and he told us lots of lies, took us to restaurants only for tourists, only hotels where he got commissions and to places where he would get paid to take us.
Travel on the train is fantastic and very cheap, buses are cheap, but not that comfy for longer journeys, but you can get air con buses, or taxis for the odd long journey you may want in comfort.
Dont waste your money on a guide, but do get the odd driver here and there, always discussing price and details before.