How Do I Analyze A BRRR Deal if I Already Own The House?

[Jeremy Melloul]

I'm a new investor and would like some help navigating a deal situation. My GF owns her grandmas house and her grandma just moved into another house so the old house is currently vacant and it can either be sold as is which is very outdated and old at the moment OR my GF and I could put some money into rehabbing it, then rent it and refi. The Estimated ARV is $400K , the house was purchased for $175,000 the current mortgage payment is $1381 with a 30 year fixed rate of 3.3% with 25 years left on the loan. I estimate it will take about $70k in rehab costs and 4 months to complete. Its hard to get accurate comps since this house is the only 5 bed 3 bath house in the zip code but based off of 4 and 3 bed comps in the area I estimate a minimum of $2k in rent. Once its rented I would refi it but who knows where the interest rates will be at that time.

I'm thinking there's an opportunity to execute a good BRRRR here but I'm having a hard time analyzing it since the house is already owned since 1999. I may be making this harder then it has to be but I'd appreciate some help/feedback.

Thanks!