The preferred mode of transportation is the Tuk Tuk. These small motorcycles or auto rickshaws are rebuilt to a 3 wheeler with more or less comfortable seats in the back, are by far the cheapest way of transportation in Sri Lanka and many other South East Asian Countries.
Some guides say you should even look out for Tuk Tuks with a meter, but we didn’t see a single one. So the best way to be safe is just to ask for the price to your destination before you hop on. Sometimes it is hard to estimate when you go some place the first time, but I would say a rule of thumb could be about 300-400 rupees for about 10-15 minutes ride / 3-4 kilometers distance. The tuk yuk guys are changing the prices sometimes.
You have to be aware that you will always pay the „tourist price“ but that’s alright cause these guys also have to make a living and it is still really cheap compared to western Taxi fares.
Also be aware in the more touristy areas that the drivers will have deals with some shops and will try everything (some ludacris storys) to get you there before you reach your final destination. Usually the driver asks you where you are from and continues with a story where some relative or friend of him is living in your country, or he has a girlfriend from there and so on …