The price for the Predator 2 novel increased a lot over the last 4 years. I got mine for like 15 dollars on ebay + around that for shipping. While others like South China Sea have been expensive as far as when I started buying these novels (2013-2014).
Only missing for me is the Predator novelization I think, from what I heard I probably won't like it, but just like in Original Sin's case(which I wasn't planning to ever buy) I might give in to take a look just due to my curiosity.