A website can cost next to nothing to millions of dollars. Most of the $ spent on those expensive websites is spent on extensive research to determine how to present their information and how users access their information to maximize viewership. It's also an ongoing yearly expense. KBB probably falls into that category...
I just read KBB was a car dealership that opened in the 1920's, and the owner made a book full of thousands of car values that he used as a reference. Someone published that information online, thus we have kbb.com. ZOMG