I went to Hobby Lobby to return something and grabbed a small chalkboard while I was there. They are really inexpensive and you can get them anywhere. Hobby Lobby's are priced at $7.99 so with their weekly 40% off coupon you can get out with it for less than $5. I'm sure Wal-Mart, Target, or Michael's offer about the same thing/price.
I painted the unfinished wood frame of the chalkboard black to make it just a little less cheap-looking. First I just brushed a little craft paint on it but wasn't really satisfied because I got a little paint on the chalkboard (I'm not very careful), so then I just took the whole thing outside and sprayed it down with chalkboard paint. Whatever works... :/
I screwed two little eye hooks into the top so I could hang it with ribbon from a wreath hanger on the front door. I think it turned out pretty charming for a cheap, fast, and easy project. I'm sure I'll use it to display lots of "Happy Birthdays" and special messages for friends and family.