It's according to how many read his blog, but probably under $20. This is based on that I might make one sale from it. 1,000 read it. 100 may click through. 1 may buy.
$3.00 is high for a 400 word article? My rate is $8.00 per 400 word article and that is low. One factor people leave out when looking for a writer is the quality of content. Most people are looking for the cheapest writer possible. I have tested this myself. (I am a writer, by the way.) I have purchased a couple of $2.00 500 word articles. Trust me. The only thing those articles would have done for me would have been to destroy my reputation. Your content is what draws readers to your site. It is also the thing that will make readers never return to your site. Your content is your reputation. If you want a cheap reputation, get cheap content. If you want to convert readers into buyers, get quality content.