Also, a writer's pay will be depend on the creativity of the writing. For example, company like Demand Media (owner of sites like eHow, Livestrong) pay their writers around $10-15 for an article. And rightly so. That's type of content that you can find on so many sites and there is very little creativity. If I were to ask someone to write a summary based on existing content, my pay will be no more than $15 for a 300 to 500 word summary. However, for my medical site where differentiation and creative writing is key (because my goal is to make it stand out from other sites with highly valued content) I usually pay $50 for a 1000 word article. My most recent article was a 3500 words which I payed $200 for.
You have to be careful also not to overpay.Sometimes I come across articles in broadsheet newspaper sites and I ask myself, 'did they really pay $150 for this article?'. Then you come across articles where you think the piece deserved $500, if not more.
In saying that, we also have to remember they have huge advertising budgets and we can't match them in what we pay. So please do not compare our rates with those of a News Corporation and what they pay their freelancers.