Newbie "ready" to buy duplex

[Byron Wise]

I'm wanting to buy a duplex for the long term.  Cash flow is everything for me and I have $150k saved.  I have found a duplex in Sacramento (where I live) that is about $425k with tenants in place and it brings in about $2285/mo.  The realtor has given me rough numbers; with $100k down and current rates, my mortgage will be about $2070.  

What I'm having a hard time with is justifying $100k investment that will bring me $200/mo.  That doesn't account for repairs, vacancy, etc.

Thanks,

Byron