just a suggestion, why not also do a car calendar??? I think that could be fun too! then those who want the calendar can purchase them.

also will generate funds too.
for the cars:
the person who wants to show their car off in the calendar would have to send you a professional photo of their car. You will approve the photo to be in the calendar. Or, you can have a competition on who will be in the calendar. (more ideas coming for that)
Another rule. The car that is going to be in the shot must have the Cars4Cancer sticker on their car. Makes it show dedication.
I am still strumming up ideas for this but wanted to throw it out.