When you get a microphone, the room matters just as much as the quality of the mic, in my experience. You have to eliminate pretty much all the background noise, or at least most of it, or recording is going to be a son of a bitch.
$50-100 will get you the Shure SM57 [i would recommend the 58 for vox though], but not the preamp. You'll need to get a preamp if you want the thing to work right. The USB mics getting recommended here are a bit different because the computer supplies the mic with power via usb, so that'll be cheaper, though the sound quality probably won't be as good, unless they've started making decent USB mics recently. I wouldn't know anything about that.