Hi Michelle,
I think you might be best using your Noosa Triathlon team to sell raffle tickets rather than use an Ebay auction if the goal is to maximise money raised for charity. I think you may be lucky to get $200 for it as is. I've seen signed balls in a display case sell for less. The display cases aren't cheap maybe $100 but I think presentation would be important.
I might be wrong but I think it is hard to reach out to peoples compassionate side thru an ebay auction where as I know I wouldn't hesitate to buy a $5 ticket in a raffle. 10 people sell sell 10 tickets and you've got $500
Good luck maybe others will have an alternate opinion.
Regards