Ok, Thank you, @BritTim. It will be a long day, but I think you've put me on the right track. (I just have to get up super early) ???? The air Fare is only 1718 baht, evisa another 1717 and a rent car less than 800 baht. What am I missing???
OR: as DrJack has suggested Udon Thani and then up to Nong Khai. Thank you both.