You can easily get a small apartment of 1-2 rooms, unfurnished, and downtown or even in Torre Alta for around 6000-8000 pesos a month.
You will have to pay electricity, cable TV, internet etc additionally.
An apartment of 1-2 rooms, if no a/c, electricity around 1000 pesos/month
Cable TV 400 pesos/month
gas for stove appr. 300 pesos/ 3 months depening on usage
Internet, depending on speed, incl. phone 1300-3000 pesos/month
There are mixtures of immigrants & locals in most areas of POP.
Downtown, Torre Alta, Bayardo, Atlantico etc etc.
The above costs I mentioned are for regular residencial areas, not gated communities where costs are higher.
You can live on 45000 pesos here.