too easy Bob, especially since the laos embassy is in KK. Get your visa in advance and take the thai-laos bus from kk, if there is one, if not, take it from udon thani, 80 baht from udon, 50 from nong khai i think, but must have visa before boarding bus, or you might get left at border, do to time to get visa at border, they won't wait sometimes. though actually, still not a bad way to get to border. bus is usually full, so will probably have to get ticket night before, if they will sell, or wait for next one. go have breakfast then come back. udon runs about 5 a day, same as NK. not sure about KK. if not, hop the train to either udon or nong khai, actaully udon better, you can walk to the bus station, plan it right and i can pick the ticket up for you, maybe.
bus takes you right to the morning market, downtown, no hassles with tuk tuk / taxis at bridge, the best way to go.
little research, apparently there is one from KK.
links below
Bus From Khon Kaen To Ventiene (laos) - Thailand Forum Bangkok Post Breaking News
as mentioned, also from udon and nong khai, 5 day r/t.