I'm not a raw feeder but if you're wanting to learn more I suggest reading around the dogforums.com and dogster forums, they both have forum section specifically for raw/barf feeding.
Also I'm not sure where you get your kibble or what 'premium' brands you're talking about but, most good healthy ones cost more than 28$ a bag (in the 30-40lbs range), but also last longer than a week. You might only be buying smaller bags, or have a smaller dog so those are definately variable factors. Many premium brands do not contain 'a bunch of junk' and I don't see what you mean by 'you don't know what's in it' because it's as simple as reading the ingredients list.
Many top brands offer grain free versions of their food and the advantage with most good kibbles is that they are more dense in calories per cup so you end up feeding less in the long run if you are in fact feeding appropriate quantities.(not overfeeding)
On the sites I suggested there have been posts where people break down the numbers and do all the math to show you that you can feed a dog a high end kibble for pennies more per day than feeding him an crappy 'grocery store' brand. I think the average is about 1.50$ to 2.50$ per day for great foods like all the Natura products(Innova/Evo, california natural, healthwise) Champion pet food brands (Orijen, Acana), nature's variety, Taste of the wild, timberwolf organics, etc...