If the Limo costs $500 and figure 3 hours, thats $1500, do they expect to cover the costs, And what if they do cover how much about the $1500 do they cover. Say they collect $2000, Is it worth $1500 in costs to raise $2000 (Net $500) , now if you say someone will donate the limo, it would be better to ask that person for a direct donation instead.
The reason you might want an event like a chinese auction that raises little profit is because it might get your organization out there to people who are not involved and that is worth something