I guess a lot of people mistake research for ripping a few facts from any source and "putting them in your own words" (as taught in many schools).
No lecturer wants to be told what they already know (which will almost certainly include the reading list and the top 5 pages from Google). What they want to know is that you understand what is being taught.
The reading list is suggested as a _starting point_. At both college and university, I was asked to do as much reading around the subject as I did lectures. So by all means use the internet as additional source, but don't rely on it as a reliable source, or as a shortcut.
If you think a book on the reading list is outdated, discuss it with the lecturer. They may not realize if a new version is released. If you don't have an opportunity to talk to them (they all have email these days), then add discussion to the essay, contrasting the book with the net. Its an easy way to pad out the research/reading section if nothing else, and also shows that you may actually know what you are talking about. It will make the essay more interesting and make it stand out from the rest.
You also don't have to buy everything on the list, get a group of friends together, buy one each and share.