Don't be fooled. Castles are so much more expensive than you think. They are heritage sites, you are obligated to keep it well maintained. This can cost between 100k to 1m per year, or even much more depending on the state and size. Next to that you're not allowed to insulate it or replace the windows with double glass, so you will spend thousands per year just not to freeze to death.
The reason these castles are so cheap is because the state is in poor condition and the current owner doesn't have the funds to fix it to regulatory standards. So you can assume you will spend 5 to 10m (if not more) into it after buying it, then to have the previous mentioned yearly maintenance costs on top of that.
I know because my French branch of the family used to live in a castle.
If you fail to keep the castle in shape you can get serious fines and even lose ownership. And depending on the country, prison time.
Then there are the taxes that are not fun at all.
So when you buy one, make sure you have at least 20m ready to spend the first 1 to 5 years. But to be sure you won't go bankrupt, better have 50m as a target as costs always end up much higher than expected. It happens a lot, people buying a castle then to go bankrupt due to the insanely high maintenance costs.
