I'm going to assume that the low price means that it's wildcaught, which means it's probably one of these:
herpwatch.org - Snakes of the Philippines
On second thought,
Cerberus spp. would fit the profile.
Edit: synonym for
C. rynchops :
Elaps boaeformis. It's a water snake and used to be called
boaeformis. I'd guess it's the most likely candidate.
"A mildly venomous, nocturnal aquatic snake, which feeds mainly on fish."