@Vinny *******
, Hmm, yep they offer a fly-n-ride to Vientiane Laos too.
It shouldn't matter much, if you have the 6AM flight there you can easily get from the Udon airport to the Nong Khai border with the mini-van parked outside the airport door. Then cross and get to the consulate before they close to turn in your application. Plus if you get the 6:35PM flight back the next day you can get your passport, enter thailand and get back to Udon in time to catch your flight back to bangkok.