There are videos of rides at the Zorb website and at Youttube. (source: Wikimedia Commons)
My first option, when it comes to saving money on a youth activity, is always to think about the possibilities of doing it, or making it, ourselves. I don't know if I should actually recommend this, for safety reasons, but I think it is possible. A quick search online didn't reveal much, but my first thought is to buy a few of those clear, inflatable, lounging beds (like they use at the pool), and several rolls of clear packing tape. Just a thought...but again, for safety reasons, I'm not sure I want to encourage this.
I think if a youth pastor called several other youth pastors from churches that were relatively close by, they could probably come up with a "partnership" and be able to buy a Zorb ball and divide it's usage time between the churches. However, as with any partnership, there are some foreseen problems with this: Who keeps the ball and where? If the ball gets ruined, who will take the blame and who will pay to have it fixed or replaced? Still, I think this is a possibility worth considering.
3. Rent it out and get your money back
Finally, I think that if a church was able to purchase one of these balls, they could easily get their money back by renting it out to other youth groups. Youth rallies, youth camps, vacation Bible schools...there are so many opportunities. If you can talk your church into making the purchase, you might be able to assure them that it will pay for itself. I suppose you could even make a profit, but I'm thinking more in terms of ministry and being a blessing.
Let me know what you think. Comment your ideas below, and thanks for reading.