Vintage and antique postcards can range in price from just a dollar or two, up to hundreds of dollars. I don't always mind spending more than minimum when the images are great and I can think of different ways to use those same images.
Vintage postcard images can be used for a variety of craft ideas for all occasions. Instead of using the costly originals, look for the numerous postcards on this site, Collectibles.about.com, and save the images to your computer.
Keep in mind that just because a craft is made for Halloween, doesn't mean you can't adapt that same idea using different vintage images.
Here are some ideas I've used in the past, along with ideas from other Guides on About.
Free Vintage Postcard Craft Ideas and Projects