Most cost segregation study companies provide the quote for free. 

There are free tools online everywhere, but basically you want to do the following:Gross Potential IncomeLess Vacancy= Gross IncomeSubtract the following expenses:Real Estate TaxesHazard InsuranceLiability InsuranceMaintenance (yes, even if you plan to DIY)SuppliesProperty Management (yes, even if you plan to DIY)UtilitiesLawncare/Snow removalLegal Costs (evictions, LLC formation/maintenance)Bad Debt (non-paying residents)City Occupancy LicensesPayment processing fees (for debit/credit cards)This will get your Net Operating Income.Then subtract debt service. 1st mortgage2nd mortgage (if applies)Line of Credit (if applies)This leaves you your free cash flow.

If you really do know the area and you think it could work, feel free to try it.  

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With one or two (or anything less than five) properties you'll be served well by the free utility of Apartments.com. 

@Faiz Kanash Rentometer is free for like 3 searches or something, so if it's just a one off, it would be an okay starting point, but cross checking it on zillow, apartments.com, and other rental sites to see the competition and activity is the best way in my opinion 

I'd love to hop on a call to discuss the are when you're free.