if you really want hard numbers, pick your favorite public university. poke around. their faculty salaries will be public record. also, the student feedback on faculty will be public record. you should be able to figure out the average number of courses taught, and the average salary in about 10 minutes after you find the relevant excel spreadsheets.
a 3 credit hour course will involve at least 3 hours of work per week (you've got to transport your body to the room the students are in). a minimum of 1 office hour per week. you've got to come up with homeworks, and grade them. even if you look at 25 students' homework for only 1 minute each, that'll take about half an hour. so it takes 4.5 hours each just to do the bare minimum possible work for a class.
google for "average college tuition" to cover that part.
what's left?