Vietnam and Thailand seem to be in decent shape right now. Coincidentally or not, now you can book flights between the two countries, or within each, for as low as B99, minus taxes and fees.

Between noon and 2pm through May 15, log on to the Vietjet website to book flights to and from select destinations in Vietnam and Thailand. That means flights from Bangkok to Dalat or Danang in Vietnam; from Udon Thani to Ho Chi Minh City; from Chiang Mai or Chiang Rai to Phuket or Krabi.
You can also get tickets to fly domestically in Vietnam for just VND 18,000 (B25), excluding taxes and fees. These are limited to three million, which seems like a lot of tickets, but still: considering the price tag, you should probably act fast.
The promotional period is limited to July 1-Dec 31 this year.