This taxi driver must be crazy! We live 95 kilometers from Ubon Ratchathani Airport. I use to take a taxi or a minivan to take me home. The going rate for taxis or vans in Thailand is around 10 Baht per kilometer. They will usually ask for 1200-1500 THB, but I refuse and say, I will pay 1000 THB and if you don't go any faster than 90 km per hour, I will give you a 200 Baht tip. If you go faster, there will be no tip. We always find an agreement on that. The trip takes over one hour. How your Udon Airport taxi driver can ask for 1800 Baht for a 15 minutes trip, makes me shake my head in disbelief. Maybe you look much too rich ?