Cheap hotels, airfare or train fares and sights in singapore-malaysia and thailand?

My friend andI are planning to go on a trip to singapore-malaysia and thailand, but were on a budget... so can u pls pls give me some info on cheap hotels or hostels in those 3 countries and where can we eat local food that is cheap BUT clean and filling...sights we can check out..and also we want to go to these 3 places via train, is it possible? any info