Some more thoughts about vocal auditions. One of the considerations is song length. I have conducted auditions where I've seen over a hundred people. As wonderful as you may be, this is not a concert, and we don't have unlimited time. You've seen American Idol. You can tell for yourself within a few notes if someone is going to be good or not. It doesn't take 3 minutes to make a good first impression.
Most directors will want about 1 minute, so plan for that best minute. Skip the recitative intro, the repetitive verses, the instrumental breaks. Find the minute of the song, even if it needs to be nipped and tucked (half a verse, straight to the chorus), that showcases your style, range, power, tone and vocal agility. No one wants to be cut off before they get to the good part, and I can tell you it is awkward for me to sit there and smile while someone goes on too long. If you show that you know what you're doing and leave 'em wanting more, it is much better than just hanging on until the director tells you to STOP SINGING, which may be just short of the part you really wanted them to hear. Do yourself a favor and plan ahead wisely. Otherwise, even if you’re great, expect to be interrupted.
You'll want to know if you should bring sheet music or a recorded accompaniment (track). Generally an accompanist will be provided, but it doesn't hurt to ask. Unless otherwise told, assume that you need to bring your own music. Do NOT plan on an a cappella piece (no accompaniment at all). Most directors don't like them (myself included), and you'll only look unprepared.
There are lots of places you can get music without spending a lot of money. Sometimes the library will have Broadway music books. Some sheet music sites will have a e-version that you can print for a couple of bucks. One of my favorites is JWPepper.com.
Amazon is a good spot for downloading tracks for about a dollar. Go to their MP3 download menu and type in the song title along with "karaoke." Preview the song you want, buy it, burn to a disc and you're ready to go. Be sure if you're using a track that you decide where you want it to begin, which will often not be the start of the song.
Sing out, Louise!