Assistant professors in my college start at $44K, with no contributions made to Social Security. Those who started in 2008 or later have never had raises. This is to teach a wide range of undergraduate and graduate courses, 3/3, with 30% of time dedicated to research and the expectation of a book and articles for tenure.
Travel funding and library budget are negligible. We have paper, printing, some xeroxing and postage, phones in our offices that can make local calls, and computers. We paint our own offices, but they are still cleaned for us so far. Offices and classrooms are heated and air conditioned 8AM-5PM on days when students are present. Our building has running water but this water is not heated, much to the shock of northerners.
Instructors start at $38K, teaching a limited range of beginning and intermediate courses, 5/5, without other responsibilities. They usually take overloads such that they actually teach 6/7, in addition to other jobs at the community college, or tutoring, or in construction. With the extra classes and the summer classes they make more total money than the newer professors. They work hard, but there is not a great deal of difference in total amount of money had and work done between these two groups.
There is a permanent war between instructors and professors about the content of the freshman and sophomore courses. The professors want more taught, but the instructors say that means more work and that they are not paid enough to do it. The professors are required to meet certain teaching standards in these courses, and the instructors are not evaluated in the same way.
Indeed, professors and instructors do not have the same class interests and that is why the lower division courses are a site of struggle. I see these things as clearly as I do because I am friends with some instructors and they articulate their motivations in a less guarded way after hours than they do during the work week.