Property on market 227 days, 3 realtors and 1 unrealistic seller! HELP I want this!

[Dana Keuning]

Hello BP crew! Let me give a little backstory on this property. It has been on the market for 227 days and has changed hands between 3 realtors who all think they can sell it for $580k. The home is inhabitable due to the current owner completely gutting it, then stopping and soon the permits they have will expire. It's down to the studs! Everything needs to be replaced, EVERYTHING all the way down to the plumbing, electrical wiring, roof, and AC. There is a hole in the roof which that alone can make it inhabitable and hard to find conventional lending. 

The home was purchased for $340k in 2021, it would ARV around 900k (if a bathroom and bedroom were added which can be done). 1139sqft
My plan would be to buy it, renovate it, rent it, and refinance it. BRRR but the payments with these rates are killing me! There are two dwellings that could be rented, the main house, and the 1 car garage that I could convert to living space (already has laundry, shower, sink, and toilet)
My estimates tell me at LEAST 200k to renovate it $275k if converting the garage. The seller still thinks they have a home worth something, but they ruined it by gutting it and letting it sit for 2 years. I don't know how to get them to realize they aren't going to sell it for the listed price, no investor is going to pay that and on top of that, have the renovation costs! 

I made an offer that was rejected, probably not even put in front of the seller either! I was told, "We have had a much higher offer and the seller didn't counter that one."
I plan to make the same or very similar offer every Monday. :)

I would be able to go up on my offer if I could find better financing options!
Private and Hard Money rates are too high! Fix and Flip loans are an option again rates are killing me on the payment that I'll have to endure while renovating for a year. I could pull a Heloc on my primary. What other options do you suggest?
The seller is offering seller financing but I'm not sure if my terms are out of the question. (3.5% amortized over 30yr, 36-month balloon payment, no prepayment penalty) or does anyone suggest something different?

Any help would be appreciated, I have just racked my brain trying to think of how I can get this home!