Joining a fraternity was cheaper than living in the dorms and was a better location on campus with parking
All I had to convince them was that my grades wouldn't suffer and that this was important to me. In the end, the membership fees were not bad at all after national dues were paid up.
If this isn't your situation, and your parents need convincing to give you the money, then show them the GPA and stats of your org. to explain the kind of (hopefully good) influence this experience will have on your life.
Option C: As suggested, if all else fails, get a job and raise the funds yourself...
- RUgreek