Honestly, I have no idea. Just know the dude bought six of those, than Johnny Depp bailed his ass out of debt and I think Nic went got into debt again. An its not just six castles, he bought a Dinosau skull, two albino kibg sized cobras, two Bahamian islands, two expensive lamborghinis, a haunted house, a luxury yacht, shrunken heads, a tombstone pyramid, 1st issue of Superman, a shark, a crocodile, fifteen estate homes around the world, an expensivr private jet, and rare art
most of that doesn't sound that much compares to what he gets.
Islands on average run around 50,000 bucks each
Cobras tend to run much much less than buying a pedigree show dog puppy and are far far cheaper than doing anything related to the care of Race Horses. Snakes also have real cheap upkeep.
Dinosaur skulls, really depends on if the dinosaur type is popular or if the fossil is in real good condition. Like Trilobites the size of your fist can be gotten for like under 20 bucks since they're so common. Iguanadons and Protoceratops are also very common and might just run you a few hundred to a few thousand at most for their skulls. he doesn't seem to hold any records from what I can see on most expensive fossil auctions.
There's no such thing as a cheap lamborghini so this could be where a ton of cash went especially on car insurance
Haunted Houses vary, usually they're cheaper than regular houses and most tend to be former farm houses. Any of the big deal haunted houses/locations don't seem to be under his name.
Yachts, another money sink so this is where another large portion of his cash could go. It's true the two happiest days with your yacht is the day you buy it and the day you sell it. It's expensive to moor them in marinas in the off season or during hurricane season, especially if the boat is big since most places can't accommodate large ships.
Shrunken heads, probably fake. The US has laws about keeping dead body parts because during the 1930's there was the Egypt craze and people bought entire mummies for family heirlooms and conversation pieces. Many were eventually taken back by World Heritage Site laws, the Egyptian Government, or Museums. Legislation passed about expanding rules about holding on to preserved bodies. There was a guy who wanted to have his skin and spinal chord turned into a hardcover leather bound book and his blood mixed with ink to write down his life story from a pen carved from his bone and an inkwell made out of his skull (he already wrote the manuscript btw). After he was dead, the family could not legally do it.
1st issue of Superman and other rare comics wouldn't break the bank compared to everything else. It's probably one of the cheapest things on the list.
Private jets these tend to be expensive to upkeep much like the yacht.
15 Estate homes, the taxes alone would do it depending on where. Unless you're shacking up in some third world country that doesn't have a functioning government that can't collect taxes. In which case you need to hire armed guards to fend off the riffraff and build huge ass walls to also keep them out, either way this is very expensive as well.
Rare Art, these were probably gifts from the CIA. Well Known Rare Art is expensive. But Rare Art can be cheap if nobody cares about the artist.
Really just the houses and the boat would be 80% of the cost of everything combined.