Replacing roof, HVAC, water heaters, etc. can certainly change the math quickly on a $100k property.That said, if its currently rented you can assume the plumbing and electrical systems are at least functional.  

One-time Expenses$1000 - Acquisition Costs (minor rehab, legal, & inspection)Annualized Expenses10% Gross Annual Rent - Vacancy Costs (turnover & lost rent)10% Gross Annual Rent - Property Mgmt (standard)$1176 - Repairs & CapEx ($1 per sq foot for tpical property)$1516.46 - Property Taxes (5 year historical average for typical property + 10%)$1000 - Property Insurance (a nice round number: seller reported that he paid $708/mo for one duplex)$27 - Water & Sewer (average across several properties from last month)$0 - Gas, Electric, HOA, Snow Removal (tenant pays or not applicable)$60 - Lawn Care (I made this number up)COMPARATIVE ANALYSIS:This is my analysis of the five properties that are being negotiated right now, listed from best to worst.Property Alpha (two-flat)$1250 - Income, Monthly (actual)$567.37 - Expenses, Monthly (estimated)$42,000 - Price, Signed Contract36% - Cap Rate (Annualized Income / Price)16.6% - ROI, After Tax (annually, assuming 15% income tax)6.0 Yrs - Until this property pays itself offProperty Bravo (two-flat)$1100 - Income, Monthly (actual)$537.37 - Expenses, Monthly (estimated)$42,500 - Price, Signed Contract31% - Cap Rate (Annualized Income / Price)13.1% - ROI, After Tax (annually, assuming 15% income tax)7.6 Yrs - Until this property pays itself offProperty Charlie (duplex)$1075 - Income, Monthly (actual)$532.37 - Expenses, Monthly (estimated)$55,000 - Price, Informal Discussion23% - Cap Rate (Annualized Income / Price)10.7% - ROI, After Tax (annually, assuming 15% income tax)10.3 Yrs - Until this property pays itself offProperty Delta (SFR)$875 - Income, Monthly (actual)$492.37 - Expenses, Monthly (estimated)$48,000 - Price, Informal Discussion22% - Cap Rate (Annualized Income / Price)8.8% - ROI, After Tax (annually, assuming 15% income tax)13.6 Yrs - Until this property pays itself offProperty Echo (SFR)$770 - Income, Monthly (actual)$471.37 - Expenses, Monthly (estimated)$62,500 - Price, Informal Discussion15% - Cap Rate (Annualized Income / Price)4.1% - ROI, After Tax (annually, assuming 15% income tax)24.4 Yrs - Until this property pays itself offNotice how the price keeps going up?

I'm looking at a multi-unit deal in Delaware County right now where the current owner pays all utilities except in-unit electricity.

The problem is that the existing home was not maintained and has major issues (foundation, sagging floors, mold, possibly a new roof and new electrical) so I'm trying to get a ballpark for what it would cost to bring the existing house up to rental quality vs what it would cost to just bulldoze it and build new, or if its even worth touching at all considering the value of the property. 

Is the electricity knob-and-tube, rag wire, or updated modern wiring?

They should be taking care of all of the big-ticket functional items - roof, hvac, water-heaters, plumbing, electrical, flooring, sinks, tubs. etc.If they are just throwing down paint and carpet, then you'll probably have a high capex in the next 5 years.James

The property looks like it was used by the previous owner as a three family, at some point; it has two means of egress (stair well & fire escape ladder) and the electric is appropriately sub metered along with kitchen, bathroom, space heater, etc.

@Samantha Klein,Please note that these products are for use with electric dryers only.Gas dryers emit products of combustion.

Each unit has been upgraded, electrical upgraded, roof less than 10 years old.  

I like using about 200 KwH less electricity each month as well.