What is the average salary of a life sciences post doc in Singapore and what is the average living cost there?
I have found that a good general source for salary information in Glassdoor.com: everything on it should be taken with a grain of salt, but it's a good starting point for getting a general sense.  Searching there at the moment, postdocs in Singapore seem to be reporting around $5K/month.

Combining that with the cost of living estimator recommended by Fabio Dias, it seems to be survivable, though you'll likely not be saving much.