$282,000 (spoiler)

Contrary to popular belief, it's never established that Nathan's entire savings sums up to exactly $282,000. He does however say something along the line when the CIA directors ask about the money transfer. But that may as well just be an expression to explain the huge amount being transferred. We'll never know if the actual sum of Nathan's entire savings is $300K, $400K or even as much as $1M. All we learn is that he makes a transaction of $282K.

Being an experienced CIA agent he deliberatly negotiates the exakt amount of $282,000 with the Chinese people so it will match the price of his house in Bahamas. Because he is aware that the CIA will find out soon enough about his transfer, and that exact figure is then easy to explain.

One can only assume that an organization like the CIA has the ability to find out where the money actually went if they really dig into it. And they'd probably see that it was transferred to a Chinese account, and not to a real estate company in Bahamas. But Bishop is already rescued by then.

The 282k was a plant from a trading account. It occurred to him to use it as a foil. He saw it in an old file while searching for Bishop papers and decided at that point to use it. It was a purposeful prop.

Chances of the same piece of property at the same price still being available would be unlikely.

Certainly would not be his entire savings. It was simply his trading accounts. A resourceful ops guy would know how to protect holdings and not to keep it under a single manager. Most convert to gold etc.

He did want to buy the Bahamas beach property. He said that he wanted to die at a warm place. $282,000 was indeed all the money he had. His banker in Hong Kong wanted to confirm Muir's true intention of liquidating all his assets. Muir spent all his money in savings to rescue Tom Bishop. Nathan once advised Tom never to touch his savings to save any of his assets.

He probably had more than that, but just picked that number to match the brochure.