Thai Airways is offering return flights to Luang Prabang or Vientiane for $231. Fares include bags, meals and seats. The only other Luang Prabang or Vientiane deal that was posted here was $199 return on Scoot but that didn't include bags, meals, etc. Great value fare. Dates are September to December 2019, excluding Xmas. Short stop in Bangkok each way.
Find the cheap dates on Thai's website then plug them into Skyscanner. Cheapest fare is by CheapTickets.