I don't think your budget will allow you to buy an interface and microphones that will be very worthwhile. One better alternative is to buy a handheld flash recorder. You can get a good sound from these - certainly good enough for a HS audition portfolio. You will learn a lot about recording as you experiment with positioning of the recorder. (Be sure to invest in whatever mount and camera tripod is necessary to allow you to position the unit.) You can transfer the recording to your computer and edit it and burn it to a CD. In addition, the recorder is a good tool for recording practices, lessons, and concerts where you don't need a pro quality recording.