I'm kinda partial to the Logitech systems for the money. Simply the best bang for the buck. I have the Z-2200 system (2 speakers and a sub) and it's plenty loud and sounds very good for what it is. Price is above the $30 target though, but you're gonna get what you pay for for the most part.
And Bose? You mean "blows" right?
As you can probably gather, I'm not too fond of them. They just use relatively crappy drivers with a mediocre amp, but in a properly designed box, and charge a premium. Their acoutiwave system simply uses a transition line enclosure design, which has been around forever. Fairly inefficient, but sounds good. A good enclosure can make a crappy driver sound great, and a bad enclosure can make a top shelf driver sound crappy.