To be honest with you, there is very little ‘out there’ purely dedicated to fossil cephalopods that is easy to obtain. Ammonites, belemnites and nautiloids are often referred to in large coffee-table books on prehistoric life but usually only in passing as they tend to dwell on the more spectacular and glamorous dinosaurs. At the other end of the scale are the research papers that are hard to obtain, unless you happen to work in a university, and even if they can be tracked down, they are, of course very technical and area-specific. Books in-between the two extremes usually consist of fossil identification manuals which are only really of use if you are actively engaged in fossil hunting.
Having said that, there are two books that I would wholeheartedly recommend:
Monks, N; Palmer P. 2002. Ammonites. The Natural History Museum.
Clarkson, ENK; 1998. Invertebrate Palaeontology and Evolution (4th ed.).Blackwell.
Neale’s book mainly focuses on ammonite biology and lifestyle and is very readable and I would highly recommend it. It is inexpensive and you should be able to find a copy for about $15. Clarkson’s book is also very good and covers all aspects of invertebrate palaeontology, not just cephalopods and mollusca, and is aimed at an undergraduate level. Although it may not be 100% up to date, it is certainly worth purchasing if you are interested I this subject. It is available from Blackwell’s publishers and costs about £22, I imagine that would be about $35. I have found both invaluable for this web-site.
For pure technical detail, the standard reference work is Ammonoid Paleobiology (ed. Neil Landman) is available. I have not got a copy but I know that Kevin (on this site) does. This is the main reference work on these animals and consists of a number of scientific papers covering all aspects of ammonoid biology and lifestyle but does not come cheap; I once saw a copy priced at £200, one of the main reasons I did not buy it! Also available is a 3 part CD-Rom available from Blackwell Publishing called Paleobase. Part.2 covers mollusca and cephalopods in great detail. The information contained there is very technical, is written by researchers at the Natural History Museum in London, and is basically a learning research tool. You will find fantastic quality photographs, some technical description, but no discussion of lifestyle or behaviour. Recommended for research only and is priced around £25, probably about $40.
There you have it. It’s not much but a start. Perhaps Kevin and Neale could suggest others. All are easily available on Amazon.