Every well written, compelling article you write with a link to your site in it will get you about 35-55 targeted visitors per month. If you write 3 a day for a week, for your blog then thats roughly 1,000 targeted visitors to your site per month. If 10% click through to your link, and 10% buy the offer your promoting that equates to around 10 sales per month per blog. $30 dollars per sale, $300 per month. Not bad for 1 weeks slow-paced work

you can easily scale it up if you have more free time. Hope this helps