Monthly Cashflow Expectations Per Unit?

[Dominic Balconi]

Hey, I have recently turned 20, and am still completely broke, unfortunately, but am slowly but surely putting myself in a position to invest in residential real estate. I have run over 100 practice deal analyses here using the BP tools, and have a simple question about my monthly cash flow expectations, so here goes:

Is expecting $500 a month per unit realistic in your experience?

Obviously, every market is different, and this is just a very general question, but I know Brandon Turner talks a lot about expecting $100 cash flow per unit a month, and I want to know if my analyses have been too ambitious. 

I suppose a good follow-up question to this would be:

What are the largest UNEXPECTED costs you have dealt with as a landlord, property manager, etc.?