Detroit. It’s a large city in terms of square mileage and very low density due to population declines since the old days. Detroit Land Bank - www.buildingdetroit.org

Would love to spearhead a Bitcoin community there, just need the funding.

You won't find houses that cheap listed on the internet. You have to go door to door and look up owners who are desperate to get rid of them. Some real estate guys make a living doing this. But, here's a link to show you some really cheap stuff in East Cleveland. Guaranteed these can be negotiated down.