First, the formulas for an income analysis (which is what investors, bankers, appraisers, and other professionals use to determine the value of an investment or business) are the same. Basically, one deducts all of the expenses--except the debt service and income taxes--from the gross income to get the net operating income (NOI). The NOI is the CFBT for an all-cash purchase, and it's the sum of the CFBT and debt service for a financed purchase.
Second, when everything is all said and done, a properly stabilized, professionally managed, income property typically will have net operating expenses in the range of 35% to 50% of the gross income. The older the property is, the closer one's expenses will be to that 50%. There is plenty of research available both on- and off-line for one to check out on this. You could also confirm this with any reputable property management companies. Furthermore, many investors (myself included) use this data to quickly assess how effectively a property is being managed.
Third, the yield (ROI in this case) is ratio formed by the CFBT (the numerator) and the total cash invested (the denominator [which included the down-payment, closing related costs, and any immediate repair costs if applicable]). If one is looking for a ROI of at least 10%, then one has to either purchase a property for at least a 10% cap all-cash, or one has to structure one's deal in a way that does the following: caps the initial cash invested, acquires the property at a high enough cap, and sets up the financing with with the right rate/terms.
I could write a lot more on this, but the goal is to show you that good deals are made--not found. It's probably good for you to sit down with a commercial agent to get a feel for that s/he has to offer, but I'd strongly recommend that you'd also attend at least one of your local REI club meetings, and network with several other investors, before you buy anything. They'll be able to tell you what they're buying, where they're buying it, why they selected the area, and how the investment(s) is/are working out for them.
Keep in mind that the numbers always work on paper; it's your job as the investor to ensure that they'll also work in reality, because it will be your dime on the line.