This is a old question of mine: How much should we paid people to blog? I`ve tried some tests on RAC, GAF and other websites like those and there were offers from $2.5/article (but they were not native-english speakers and their grammar was much bed than mine) up to $15/article. I`m interested: How much would you paid someone to blog? Per Article?
You can see exactly how much per article for the type of article you want at http://www.BlogPayz.com There is a tiered price matrix dependent on exactly what the advertiser wants from the bloggers regarding his niche.
You gotta have some criteria or standards first to determine if the article is worth a dollar or not. If the article is of good quality and it matches your standards then set a price, this may also depend on the market value of the writer of that article if he's already an expert or not so it may actually vary.
Depends who you're asking, eh. If you ask someone that's a relative newbie, poor at English and all, you'll probably get people at $1/500 words. Ask someone that's blogged for a while, is good at it and has a reader base, and it'll cost $50+ Course you do get those in the middle that charge $5 - $20.