What about edible favors? Those dont typically cost much. You could make chocolate lollipops or cookies shaped like car with icing in one of their colors? I dont know if bridal shower favors are necessary but I think its nice to thank the guests and I hate trinkets as well so for my bridal shower in a few weeks my BMs decided to go the edible favor route and are making these:
http://www.marthastewart.com/sugar-cookie-cakes