One school where I used to work paid their instructors $1800 per course if they had a Master's and $2100 per course if they had a doctorate, and I gather they're on the mid to upper end of the scale. I occasionally teach for a resource-constrained rural community college that pays less than that, but I don't do it for the money, I do it because I appreciate the school's mission.
If you put in the number of hours that you should, you end up making the equivalent of a pretty low hourly wage. I've seen people do the numbers and realize that on a strictly total-pay-divided-by-total-hours basis it would have made more sense for them to make cappuccinos at Starbucks than to teach university courses as an adjunct.
In other words, if you do it, it's best to haev a motivation other than money. If you want it as a bullet point for your CV, or if you just like teaching, for example, it can make sense.
-=Steve=-
B.S., Info Sys, Charter Oak State College
M.A., Educational Tech Leadership, George Washington University
Doctor of Health Education, A.T. Still University, in progress