Negombo is compact enough to cover on foot along the beach strip and colonial quarter. Tuk-tuks are everywhere; fares for short hops within town should be 100–200 rupees. Agree on a price before you get in — meters are rarely used, and drivers near the tourist hotels will quote inflated rates as a starting point.
Bicycle rental is widely available from guesthouses along Lewis Place, typically for around 500–700 rupees a day. Cycling along the Dutch Canal bank is one of the best ways to see the surroundings at a relaxed pace. The flat terrain makes it easy.
For longer excursions — out to the lagoon villages or south to the airport — a tuk-tuk hired by the hour or half-day is the most flexible option.