Appraisal issue for dream home

[Timothy Solomon]

This is for a dream home in my “dream” location. A run-down duplex (that is deeded as two single family homes) is on the ocean, surrounded by 8+ million dollar homes. Due to the uniqueness of the opportunity, (there are no comps), I believe the property will appraise for 2.2 million. There is no agent and no broker. The seller and I agreed on a price of 3 million. Bank will require me to put down 25% of the loan. I can afford the down payment but I can’t afford the additional 800k to make up the difference. The seller agreed to seller financing but the bank will not allow that. 

What options do i have! Does anyone know of a bank that will allow for this? The property is a slam dunk and can only increase in value since it’s on the sand. I would be selling my primary residence and would live here. Alternatively I could use it as a commercial property but the bank would require even more money down for that. 

Also- any advice on trying to get it to appraise for higher? 

What are my options?