Can anyone recommend any good books about The Exorcist (the original film)?

(Obviously, I have an interest in Centipede Press's The Exorcist: Studies in the Horror Film, but that's hard to find within my budget).

These 2 popped up quickly on Amazon:

- The Exorcist Legacy: 50 Years of Fear by Nat Segaloff

- The Devil Inside: The Dark Legacy of the Exorcist by Carlos Acevedo

In general, they seem to be what I'm looking for, but the page counts seem a bit thin (sometimes - though not always - that's a marker of pop culture-type things, which is very much not what I want).

Any suggestions appreciated.