anyone has cheap source to recommend...
Scuba-diving I supposed?
Why not flip through Yellowpages and decide from there? Also, remember, cheap doesn't necessary mean that its good. Make sure that ain't any hidden costs, especially for gear rental and certification as well.
Are you looking to get Scuba gear
or do you want to learn Scuba?
As far as I know, all the schools in singapore charges all the same price range for Open and Advanced Open.
The variance is about 30-40 dollars lah. All of them teach on the same syllabus.
So I don't think paying more necessarily get you better training.