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

WHAT IS A COST SEGREGATION STUDY?

These methods include: Detailed Engineering Cost ApproachDetailed Engineering Cost Estimate ApproachSurvey or Letter ApproachResidual Estimation ApproachSampling or Modeling ApproachExperience or “Rule of Thumb” ApproachIt’s important to understand the differences between the approaches including which one best fits your property and the reliability of each approach.DETAILED ENGINEERING COST APPROACHThis approach compiles the costs from construction and accounting reports to build a report.

To save those costs, you might want to stick to some year build and older, for example, if you cannot do inspections on the properties that you are buying due to off-market deals or something else that is hindering you (all sellers I buy from do not want anyone in the home till we close).

However, I still struggle to understand the art of estimating rehab costs. 

For residential multifamily properties (1 - 4 units), can you use a home warranty to take care of the repair costs associated with rentals?

Here's an article with FAQs including the cost of a study.

Is there an easy way to divide the basement up? Each side of the duplex has access to the basement but below everything is connected together and I want to make sure no side has access to each other. The way I can ima...

Also, what are some other low cost amenities that I can add to my STR that will yield a higher ROI?

First off DO NOT slash prices yet!