There's many ways - traditional banking being the route I took. Initial sunk-cost was $350k, interest rates were low, and my loan amount was small all things considered. I had most of the cash on hand and collateral in the form of a house. I did all the building and excavation myself, the only things I subbed out were plumbing, electrical, HVAC, and some drywall because I really don't like drywall.

Also fortunate because the last few years has seen a huge run-up and appreciation in property in my area specifically where the median house price 10 years ago was around $250k, it's now just under a million for a run-of-the-mill 4 bed, 2 bath, 2200sqft home. The buyer was a small investment company from out-of-state which is really unfortunate because I was hoping to sell to someone local but given the offer they made me, no one could match or even come close.