One issue that I'm noticing is the range of reported insurance costs.

You can always consider doing a cost seg study on a property that you buy and that can also help with tax benefits if you cannot qualify for the real estate professional status.

Negotiating favorable terms like a low interest rate or interest-only payments for the first few years could help manage cash flow until renovations are complete.

It’s a lower risk strategy since you’ll be living in one of the units, and you’ll qualify for low down payment loans.

Investing in a low-crime area.I'm not being facetious. 

When a PM does charge a markup, he's usually getting a discount on the service to keep the cost stable.

With that said, the income can still offset the cost of holding the property as a long-term investment.

Cost approach A straightforward method that adds the cost of the land to the cost of building construction.

Let's say at 6% over 30Yrs will be about $960 per month(Principle/Interest) with the remaining  interest only portion $40K costing roughly $200 per month. $1500- $960 + $200 IS $340Cash in your pocket after everything roughly $1500-$1160-$340 which is not bad for a 100% financed deal(INFINITE RETURNS)Now, If you ran this analysis on a 1% deal as @Nicholas L. mentioned you will undoubtably end up in the red each month.All the best!!!

Is there any good rules of thumb to estimating the cost of a boiler?