Although the airport is called Ubon Ratchathani International Airport, this small airport in the east of Thailand only serves domestic destinations to Bangkok. Next to being a domestic passenger airport this airport is also a Royal Thai Airforce Base and was used by the Americans in the Vietnam War.
The airport is located very near the city, just 1 km from the city center, at the northern side.
Best to go to one of the taxi coupon stands in the arrivals hall and buy a taxi coupon for 100 baht that will take you to pretty much everywhere in Ubon. Alternatively you can walk across the parking area to the waiting tuk-tuk drivers but prices will be about the same.
All prices quoted here were found in July 2017