There is no real way to answer your question honestly because there are simply to many variables to consider. Do I think you can be in a postion where a network of 10 blogs were netting a sale a day each within a year, probably.
But you have a large learning curve if your going to do it. Promoting a blog is similar to promoting a free site in some ways but it's also very different and its really more than just writing good sales text.
But if you want to really get serious about it, start reading there is tons of stuff out there about marketing with blogs and then try and disect what Boogie did with Pornogomy because that definately one way to be successful at it.
Here's one of the places I like to read now and them
http://blogforfunandprofit.blogware....g/HowToBlog101