No, it is not easily to earn $5 - $20/article like what you said above. This price is for great website with huge traffic, (or may be page rank). The length always be 300 -500 words, and always be check for unique. This is not an easy money maker methods for newbie.
You get what you pay for... I'd rather have quality articles that provide value to the reader.. so they will be comming back to your website.. then you become an authority with your subject there fore people trust you more..
yes of course it is possible. but there are some important qualifications : you have to be a native English speaker and if you live in USE then it will be just awesome. you have to have a great experience in this field. you should have some published articles in the popular sites. so you have be the professional article writer .
From my experience it's not easy at all to find a good article writer, especially when your product is very niched. So guess it's no easy money for a writer either