One point no one has brought up, and I think it could cost bucks?... aand that is to provide some sort of music...either a live band or a DJ.
Do you guys/gals think that this is important?
Thanks for the feed back to date.
CC68, as a person involved with music in several different forms, if I were you, I'd simply get some good speakers/small PA system. You can get a fairly decent set-up for a reasonable price. This will include a microphone so you can do appropriate announcements, etc. If you plan on doing this yearly or several times a year, you'll save yourself a ton of money in the long run. Plus, if you use a local shop, you might be able to get a good discount or donation in exchange for a event sponsorship.
From there...as far as music is concerned, I would simply get an iPod and create a great playlist that is long enough to last the entire event. I wouldn't waste money on DJ for this type of event. People are busy talking, looking at cars, etc. and although they'll enjoy the 'background music', it'll be just that--background music. The expense just doesn't make much sense.
Unless you want to make a band a major part of the event--end of show party, for the same reason, I just wouldn't spend the money. I personally go to these shows to see great cars and meet cool people, not see some 4th rate cover band (for some reason I'd always prefer to hear the original recording than a bad version of it)