I'd say it doesn't just depend on location, but often on the toolset the candidate has experience with, the toolset they've got experience with, and how much coding knowledge they have outside of whatever might be used for the tool. Graphically speaking it varies a LOT in the US - the same position in the Northeast or parts of California can sometimes pay as much as double for a similar spot in the south or middle of the country.
I'd just check out computerjobs.com and search in some of the major cities - there should be enough folks who list actual salaries for you to get a general idea.
What kind of action and against whom? I'm sure many would take action if their company was involved, but if that's not the case, there's very little anyone can do - you can't randomly acccuse companies of this practice unless you're involved in it somehow first hand.