Circle Chase was first (with by Joe Mad and Fabian Nicieza) and then Sins of the Past (by Mark Waid and Ian Churchill). The reason it's so expensive was because it was a very low print run, done years before trade paperbacks were common, so it's kind of hard to find. The back issues, however, are not, and you probably could have got all four issues for $10-15. Since it was an early trade, it also doesn't have the greatest binding int he world. At least you didn't pay more.