As the father of a 15 year old I know there is a way to afford ballast if you don't buy any more songs on I Tunes and don't get Rock Band. I have a 93 205 that we surf with. Here is the set up. 1200LBS in a couch in back with the seat out, 400 on starboard side and 400 in the front with any other riders on the engine or on the starboard side. Look on e bay and you can get deals. Have the driver go about 10mph and just dial it in from there.
I second the ebay idea, you can get some good quality sacs for very little. I bought some launch pad v drive sacs for somewhere in the vacinity of $20. Bought them when I was messing with the weighting and kept them becuase they do the job just fine. The pro series sacs are by far the best I've used but the others work well enough when you're on a budget.