Thomas Asbridge's The Crusades would probably be what you're looking for. It's a brief summary of the first major (numbered and in the Middle East) crusades and their effect on both Christian states and Islamic ones. It's also both relatively affordable and written for a wider audience than a more academic work on the subject.

For an introduction there are a lot of options. *The Crusades, 1095-1204 *by Jonathan Phillips is a good choice. The Crusades: The War for the Holy Land by Thomas Asbridge is similarly good. The Crusades: A History: Third Edition by Jonathan Riley-Smith is a bit old these days but still good. All those books are basically the same; they're written by academics who taught the crusades at their respective universities with an undergrad level audience in mind.

You could also go for the lengthier God's War by Christopher Tyerman, which is more advanced than those books but for that you get more detail.