In Port Vila the buses are van and mini-buses with a red B on the left side of the number plate. They largely traverse the main road take you directly to your destination. There are no scheduled services and are perhaps best thought of as cheap, but shared taxis. Wave at them to stop one heading in the direction you want to go. They are plentiful within the city and outside the city you can usually arrange for a bus to meet you at a particular time. If one looks full, just wait for the next one. The buses are used by locals, but are very friendly, cheap, and easy to use by tourists. Fares are usually calculated per person. The cost is usually 100 vatu per person unless you are traveling a longer distance, e.g. Mele Cascades - in which case expect to pay 200 vatu per person. There are significantly less buses on the road on Sundays.
Taxis are plentiful within Port Vila. Fare is calculated per taxi. There are standard fares for journeys to and from the airport to most accommodation around Port-Vila a list of which should be available in the arrivals section of the airport. 1000VT to the city centre as of August 2007.