How do I even start to estimate the money needed to get this property in a salable or rentable condition (I am open to both)?? The house that was built in 1940. It is approx 1300 sqft. It has no HVAC system and no insulation. I am sure the electrical needs upgrading and I will need to add a bathroom to make it comparable (3bd/1ba). It has been vacant for several years. There are no structural issues to my knowledge. Any advice would be appreciated.
You should read up on the subject as much as you can (J Scott has a good book on this) in order to get a better idea of the general price of repairs. Secondly, you should walk the property with a contractor and get a bid. Follow this person around and take notes on everything you're told and over time you should get, at the very least, an indication of how to estimate repairs and timelines for these repairs.
In addition to walking the property with a contractor, you could try to partner up on the deal with another investor who has experience with flips/BRRR. Then you have someone else to lean on for advice on estimating repairs plus every other little detail that goes into turning over a property.