Have you thought of AirAsia www.airasia.com for BKK-HAN, Air Asia HAN-KUL, Air Asia KUL-REP and Bangkok Air back to either Chiang Mai or Bangkok? A little playing around may reduce the price so that it is more palatable. The downside is more times on airplanes due to going the opposite direction to get to REP.

Another AirPass alternative is to try the alternative routing into REP via either VTE or Chiang Mai. VTE can be somewhat of a pain, if you decide to save money by crossing into Thailand and fly very cheaply out of Udon Thani or take the over-night train from Nong Khai.