KT:
Considering that you will be there for only 5 days I would recommend getting a place in either Ibiza town (Eivissa) or Playa D'en Bossa. Yes, Playa and Eivissa are more expensive that Sant Antoni, but the price delta between what you would pay in SA for 5 days, and what you would pay in Playa or Eivissa will not be more that 100E - 150E. Since, you are not alone the price delta is halved.
Since you are coming all the way from the US, I would recommend that you extend the stay to 10 days. Unlike for our European counterparts, the plane ticket alone will be around $900-$1000 per head, if you are coming for the West Coast. Hence, it is not a trip that most Americans will make every year, especially considering that there is so much more to see in Europe. 10 days will give you ample time to catch the opening parties, relax, and see the island. You will not have to come back regreting that "we should have stayed longer, etc."
I was there from Jun-18 till Jul-02, I caught all the opening shows, saw a lot of the island, had time to relax, and I came back with only a one regret; not being able to see Es Vedra. I stayed in SA only because I went solo, and I did not want to spend most of my dollars on lodging. In most cases you do not need to get a cab, or even if you do, you can share a ride with others. Don't get me wrong, SA is not bad as some make it out to be. There are quite a few bars (like the PussyCat, where I had great conversations while enjoying my favorite Warsteiner for only 2.40E for 0.25L). The bus ride to Playa which was no longer than 50 minutes (including the bus change in Eivissa), which worked out fine as I could take a nap. However, given the option I would rather stay in Playa or Eivissa as I loved going to BoraBora which is in Playa.
There are a few places near ElDivino/Pacha, which are quite reasonable, and it is very central too. There is a great bar on the corner where the street curves towards Pacha operated by some Germans (One of the guys, Stevie, is pretty cool). It's a great place to sit back and sip a few drinks while socializing with some interesting folks. McRackin, can you please help with the picture and name of this place.
Cheers,
LagunaBeachCA