We have had natural disasters or unforeseen complications in our condo building.

I’d start with barring unforeseen circumstances in regards to your quote on the outlet (my preferred method since it allows for different brand EVa as well as high end air compressors,welders, etc.) you’re getting hosed. 

Once you've done a few properties like this you'll be able to do rough estimates on your own.As for a formula....that obviously depends on the condition of the home, the finishes you choose, and who your contractor is but, in my experience, you can expect to pay $20-30/sq ft on average barring any huge unforeseen expenses - for a retail flip.For a rental, its a little more complicated but usually you'll spend significantly less getting a rental property market ready.

While, as we are seeing with COVID, unforeseen circumstances can happen, there are some things to consider

The death was unforeseen.

This exclusion can be used once every two years.Partial Exclusion for Reduced Use: If your dad is selling his home due to a change in health, employment, or unforeseen circumstances before meeting the two-year ownership and residence requirement, he may be eligible for a reduced exclusion based on the time he lived in the home.Purchase of a Smaller Home: While your dad intends to purchase a new home worth less than his current one, this won't qualify as a 1031 Exchange (like-kind exchange) since personal residences don't qualify for this type of exchange.

Where if you are financed on the FHA loan you will need to keep that house because your loan amount is too close to the purchase price.When I talk with my clients I look for the most flexibility to protect their portfolio and give them exit strategies if somethings unforeseen happens in their life.Tim ** I would encourage you to take out a bigger HELOC say, $150,000 to $200,000 but only borrow the $93,400 or what you needed to make the purchase happen.

Unforeseen expenses can reduce profits significantly, necessitating thorough property inspections before purchase.

The pillars of our local economy remain strong and improving, large amounts of migration to Texas cities is still in progress, new businesses are arriving (especially like the California giants making the leap to Texas), positive COVID vaccine news, and all the things I mentioned in the post should hold firm barring any major unforeseen meltdowns. 

I'll add another unforeseen hurdle- Pain and Suffering.