New lines to the water heater, laundry, bathroom and kitchens.

Although things could be a little different for me in the Midwest I do this same thing with a cheap rate and monthly discounts and my income is 1.5-2 times the amount I would normally get renting the units out long term.

The MLS is a great place to start but finding off-market deals is the best way to get a discounted price.

IRR is looking at all those cash flows paid back to you (these could include distributions from operations, refis modeled, and sale proceeds), and calculates the discount rate to bring the net investment to zero.  

For what you're talking about going from a ~1,000 sq ft house to almost ~1500 is a pretty material difference, as is adding that second bathroom. 

I've never had two bathrooms.

I paid $40K to put in a kitchenette and bathroom and it gross'd $1900/mo. 

Do not discount the benefit of appreciation. 

Anyhow, this past June there was a fire in the bathroom ceiling of the apt. next to mine.  

Then all went down hill but we took time of vacant to renovate bathroom and rented to a family for $1000 a month.