I would look at why an appraisal comes in low.

It might be a good idea and it shouldn't cost too much as it is all computer generated.

I've done my fair share of research into good 'rules of thumb', but not any that consider the cost of land in the area.

@Samson OniI would ask for a credit for the amount it would cost you to fix.

Not doing an inspection is going to hurt you, especially on this low priced home.

Looking for something that helps factor in all variables, fixed costs, interest paid on hard money loans, reno costs, etc etc. 

A Real Real Estate AnalogyI am starting my real estate adventure and I am trying to draw a comparison from paper assets (stocks, bonds, notes, T-bills, crypto, etc.) with real estate.For those who know a bit more than me (and i know this will vary by person) but what are corresponding "tech stocks" (AMZN, AAPL, NVDA, FB, GOOG, etc.) of real estate?

This AC costs $17000 in 2020 and assume will no problem for a long time but most expensive one and shortest time died. 

Are there any red flags I should be aware of, such as the vacancy expense or NNN costs?

This process can be very costly, requires zoning permission, in addition to all the items you listed.