After doing the Top Trumps last year, make sure you leave plenty of time to get it all done if you have a deadline.
You could get one done for Christmas, perhaps find a way of having a sponsorship on each month from 12 EK9.org Vendors with a company logo and web address in the bottom right-hand corner and ask for some sponsorship to keep the cost down for everyone who buys one because with only 12 pictures there will be a lot of people buying a copy without their own car on it and will want to pay as little as possible.
I'd aim for £10 delivered, £15 max. But I'm not sure how realistic that'd be for a small batch.