The reason being every site and project is unique, and while I do attempt to provide a reasonable estimate of what it will take to complete your project there are many factors outside my control.

What are good strategies or online calculators to help make rehab estimates? 

.); the sufficiency of estimated insurance proceeds from ordinance or law insurance and other coverages to repay the Mortgage Loan in the event of partial or full casualty, or condemnation; and for a Tier 3 or Tier 4 Mortgage Loan, if requiring execution of the Limited Payment Guaranty (Form 6020.LPG) would mitigate the risk of the as-rebuilt Property not supporting a Tier 2 Mortgage Loan.

(Typically estimate between 2-3% of the loan amount in closing costs: appraisal, credit report, points/origination, underwriting/processing fees, title fees, prepaid taxes and insurance etc)I am sure there are others I am not remembering

Getting a full, locked loan estimate is the only way to truly compare the two. 

Like most wholesalers, they over-estimate their ARV and underestimate their rehab costs.

I have no experience estimating rehab costs and I know costs have drastically changed since books like J Scott's were released. 

You must call Airbnb before you do that, and send proof of repair issues serious enough to require cancellation (photos and repair time estimates) BEFORE you cancel on the guest. 

Stick with the formula, because your ARV isn't necessarily the end buyers ARV and same with repair estimates.

My estimated property value is $1,300,0000.