Firstly I think it depends on your expectations. Do you want to save money? Do you wish to maintain or approximate your lifestyle at home? To give you an idea of the cost of living look under properties here to give you an idea of rental and look up
www.coldstorage.com.sg to give you an idea of the cost of food. Schooling has been a topic in the last couple of days. Other factors are electricity(there is a website where you could do a rough estimate) and transport. What we spend for a family of five would be considered higher end I guess and much of it is paid by the company such as rental, schooling and transport. This would perhaps give you an idea:
Rental(3 bedroom)- $2500 to $5000 per month(Housing board apartments are cheaper)
Electricity- $200-$400 per month(we use more though)
Car-$1500 up per month rental, public transport and taxis are cheap though
Schooling- local(a couple of thousand? unsure) international school $10000 to $15000 per year
Groceries- have friends who use $200 or less per week, but we use $400 up per week(I'll be shot for this!)
Medical- expensive need insurance-unsure
Many of my friends live on a lot tighter budgets than our own and are very happy-it really depends on the type of compromises you are willing to take. We had been expats before in a difficult posting which I loved but now with more children I am unwilling to make the same sort of compromises we did then.