The going rate for a technical article written in ~4 hours is $500? That blows my mind. I'm not saying it doesn't happen -- I've only done non-technical articles -- but that it's hard for me to imagine it being profitable for the publication.
800-1000 words produced from scratch in 4 hours, including research, editing, and graphics, is going to be garbage one step above what you'd find in a content farm. The same derived with minor modifications from an existing article will be little better than scraped content.