Obligatory answer: No, it doesn't cost anything to edit Wikipedia. In fact, if people were paid to edit Wikipedia, that would throw off its objectivity. For example, Fred Smoot, of the infamous Minnesota Vikings party boat scandal, would probably love to pay money to get his name delisted from that article, or at least have the article "professionally edited" in a way that makes him look better. But according to the Wikipedia article, we know that he got fined the equivalent of one game's salary, which is $82,352.
Speaking of salaries, I read through the Form 990 filed by the Wikimedia Foundation. Sue Gardner, executive director of Wikimedia, is paid $75,000 per year by the Wikimedia Foundation. Mike Godwin, general counsel, is paid $56,667 per year. (Or is that just for half of 2007?) Brion Vibber gets $62,473 per year. Jimbo Wales doesn't draw a salary from the Wikimedia Foundation. If he makes his money from speaking engagements or from Wikia, that doesn't count against the charitable donations sent to the Wikimedia Foundation.
I earn more money in a year than Sue Gardner, Mike Godwin, or Brian Vibber. I guess it pays to be in the private sector and to have a job where I have unique skills in the company. I don't think I'll ever earn as much per day as Fred Smoot does, though.
EDIT: Before anyone calls me a teenager, I'm only three months younger than Jimbo Wales.