From the windows, I saw there was a big mess inside the house: very dirty carpet; old and dirty furniture randomly stacked on each other; all kitchen cabinet drawers were pulled out; no clothes, dishes or food, no any sign that someone lives there.

I want to get this thing going but this fear of not knowing my rehab costs is making it very difficult to run numbers and pull the trigger.

And still do your home work before pulling the trigger.

Especially if you are able to rent the property out and pull equity and still cash flow.

Get ready to be razzmatazzed and then get ready to pull out your credit card for the $10K-$40K coaching pitch.

The house is usually extremely dirty after one year - with the same air filter installed -(after I show them how to change it at the lease signing, and it is spelled out to change four times per year), weeds in the yard ( too hard to pull them out as they become big I assume), many times- cars parked half on the grass ( we always have two car driveways and garages - and it is spelled out in the lease not to do this), etc.

If you only have 20K invested and the bank has 80K, they will be more hesitant to foreclose on a house they have an 80K stake in, whereas if they only had a 20K stake in the house (you have an 80K stake) they will pull the trigger easier because it is less of a loss. 

I would not pull the trigger on this one.

You can immediately pull out your initial purchase if the LTV is there.

There are many other factors that you can pull into the software that Zillow provides for free (zillow.com/research/data/).