Regarding inexpensive stethoscopes, a Littmann Lightweight SE can be found for around $40-45, I recall. A website for MDs reviewed about a dozen stethoscopes, included several inexpensive ones. Surprisingly, a $19 Sprague was highly rated. Here is the review in full: http://www.forusdocs.com/reviews/Acoustic_Stethoscope_Review.htm Aastha
Here are examples and discussion of course crackles and pleural rub (and other breath sounds) ... http://www.easyauscultation.com/course-contents.aspx?CourseID=201.