Owner occupied multi unit - calculating financials

[Chris May]

My wife and I are looking at a few duplexes and triplexes in Oakland/Berkeley for owner occupancy. I was curious what methods other people use for evaluating the financials of these deals.

I was thinking I would just consider the mortgage + expenses - rental income as our "rent" and compare that to market rents for similar properties in our area in order to come up with an offer price. 

Anyone else have another approach? Even using that approach I'm worried we'll still be coming in at the low end of the offers received on each property. The market around here is nuts right now.