Hey Pipelion,
Here are a few additional ideas re: sponsorships...
1. You may also want to try & get sponsorship from companies dealing with performance upgrades & even throwing together a sponsorship proposal to any of the smaller companies that GT owners buy all their "extras" from. I don't know what the competition is, but they may want their name out there. We do this all the time in skydiving, including when we make our DVDs & it works great!
2. Some companies will want to throw in $300, some might want to give $3000 or more. Depending on the amt they give (ie, if > $4000), you may want to allow an ad as opposed to just throwing their logo on the place where it will say "sponsored by..." Extra incentive...
3. Finally, is this something that will just be bought by those that go to the rally or is it something that will be sold to anyone interested (not just on this forum)? If it's going to cost that much & be professional, it might be something that other GT enthusiasts or people not going would want to purchase. The potential to sell 1000 rather than 100 might also make a difference to potential sponsors (the more who see their name the better)...
Good luck!
MJ