Living expense for a single person in Singapore

Well, there are many (foreign) workers her who earn S$600 or less per month and send most of that home to their families. So I guess that gives an idea of the minimum, although I have no idea how they do it.
For a frugal single person with a student lifestyle (which means sublet room, no entertainment, plain food and no travel) S$700 rent and S$600 for everything else might be manageable, but not enjoyable.
If you want privacy, an own apartment will cost you S$2000 or more. Occasional restaurant visits, activities, taxi rides and beers will easily triple or quadruple the budget for others.

A fresh university graduate earns around S$2500 a month. With an MBA and some experience you might get S$4000-5000. But it is currently very difficult to get an employment pass (= work visa) and hence to find any employer willing to consider hiring a foreigner.

Hope this helps!