I don't know Vietnam, but their yachting infrastructure has only recently been developed so I would not expect much there yet. Judging by your own website, you should know this already so why are you asking the question?
The main yachting centers of SE Asia are Phuket, Thailand and Singapore. To a lesser extent, Langkawi in Malaysia.
I suspect that South East Asia, Thailand, Langkawi, Malaysia will be good places to pick up a bargain. There is quite a cruising fleet backing up of those not able to go up the Red Sea due to the pirates and too worried about the trip around South Africa to go in that direction. I might just slip over there, have a holiday and see what is available.
Neil and Ley Langford have posted this on their website on behalf of Pete and Kathy on SV Wave Runner :
"We have negotiated a discounted rate of $800/foot with Sevenstar, sailing early March from Phuket, Thailand, to Marmaris, Turkey. This is the same company that shipped so many yachts from the Maldives early this year, and from Phuket later in the year."
So for a 40 footer it would be $32000
Quite an incentive to think about giving up & selling the boat in either Phuket or Langkawi.
There's a Boatshed franchise there (Boatshed Phuket), I spent a year or so around there a couple of years ago, all sorts of boats around for sale, as already said Phuket and Langkawi, don't know about Singapore...