Buriram to Chiang Rai is a long way.
Agreed, you are not going to have much time for Isaan if you do this trip. Chaing Rai is a night, Pu Chee fa also a night. If you are there why to go to Chiang Khong on the Mekong as well.
This winter we flew to Nakorn Panom and rented a great one year old Yaris that got 20 kilometers per litre for 750 baht a day. Did NKP/That Panom, Mukdahan, Sakorn, Nong Khai and back to NKP. Lovely and made all the better by cool season. Temps were 14-28 degrees, literally heaven