In the Raleigh, NC area mid-to-3/4 high-end custom homes in the 4,000 sq ft area w/ 3-car garage run around $175 to $200 per sq ft including the lot with lots running typically from $100,000 to $150,000. That means the build portion of the cost is typically in the $140 to $175 per square foot range.
Another popular theory is that the Joker is Jason Todd a.k.a. (another) Red Hood a.k.a. (briefly) Nightwing. Jason was brutally beaten to death by the Joker in 1988's 'Death In The Family' storyline. In all honesty, this would be a little difficult to explain: Jason Todd beaten to death by the Joker who happened to be Jason Todd all along.
1 The Joker - The Joker is the main antagonist in the game. He is captured by Batman and taken to Arkham Asylum but escapes and takes over the asylum.  Dr. Harleen Francis Quinzel/Harley Quinn - Harley Quinn appears in the game already loose in the asylum. She helps Joker break free and cause mayhem on the island.