Originally, Mark was prepared to spend the market price of 25000 gold coins on buying that 5-acre land, indirectly wasted all because of him.
But, he didn't expect that the Emperor would make this land for his private use to test or demonstrate the weapons as he wishes for free. That means he doesn't need to pay a single copper coin.
However, the land will not be owned by him but belonged to the Empire. So, he cannot sell or rent it to any other person. This is something that he doesn't understand as the land doesn't have any strategic value to it.
Mark didn't know that the Emperor was forced to do it under the pressure of the court officials as it was originally supposed to be auctioned so that it can be turned into an elite neighborhood where wealthy commoners can do their businesses.