Is it really so expensive in SG that you can barely survive with 3k SGD? What is the cost really?

Per month 3k SGD vs 5k MYR, assume net for easy comparison. Just look at the minimum requirements for survival:
1. Room rental: 500 SGD vs 500 MYR
2. Transport: 100 SGD (train/bus) vs 1000 MYR (car, toll, petrol, maintenance, parking, insurance)
3. Food: 450 SGD vs 900 MYR
4. Phone: 30 SGD vs 50 MYR

Balance: 1920 SGD vs 2550 MYR for your shopping, entertainment, support parents, whatever else... pandai-pandai manage lah. I think both sides can save 1k SGD/ 1k MYR with some smart budgeting.

So if you are single, SG is an easy choice. Personally I didn't choose SG because already have family and when you have family you can't simply budget like this. All the extra costs in SG will go up a lot compared to Malaysia with family.