I gambled on the cheap solution and lost.

The detailed methods are the most accurate, most defensible and get the most benefit.

Do you know how I can get accurate quotes?

What is the most accurate site?

Will they be able to offer up a more accurate assessment of ARV when needed?

For my own reno projects, it took years to learn accurate construction costs and assemble a scope of work.

I need an accurate estimate of what absolutely has to be done just to stabilize and get in rentable or livable condition.  

A Solo 401(k) is a qualified employer retirement plan, and needs a legitimate business activity with no full time employees to act as a sponsoring employer.You can read all day long on BP and get into paralysis of analysis, as well as digest some less than accurate information on the topic, to be sure.Alternately, you can read up a bit, with the goal of identifying a few professionals in the field, and then get on the phone. 

I only use Rentometer for accurate rent estimates. 

Hope I understood your recommendation accurately?