American Psycho. The movie is excellent. The book is fucking disturbing. Wasn't prepared for the necrophilia or cannibalism.
I think the movie got it right, just disturbing enough to see how nuts he is, but keeping things in normal horror movie realm.
I get hardcovers of series I really like, otherwise it's usually paperback.
But I did spend AU$120 to get the last book in a trilogy that had been eluding me. The first two books I got for like $20. Couldn't find the third anywhere for years. The only option was this omnibus edition with all 3 books, at Au$120 on Amazon.
Glad I got it, I can still see it on Amazon but now for around $300. It's not a well known trilogy, the Deepwater trilogy by NZ author Ken Catran. I read those books so much as a kid that I just had to read them all again as an adult.