Anyhow, I stole this idea at mommy's group that I joined to and most of them made their own birthday chalkboard poster for their little one and some just bought it at Etsy. As me of course, I like doing things like this and since I am a DIY junkie myself :P.
So, if you wanna Do-it-Yourself as well. Here's what you need:
black foamboard from dollar store $1.00
sharpie paint pens $6.99 @ Michaels (they always have coupon for 50% off regular price)
This would cost about 10-15 dollars depending on how many paint pens you're going to use. Which is not bad compare to the ones that are sold online.
Here's how: (The picture is pretty much self explanatory, but let me know if you have any questions)
Print, Tape, Trace and Write....that's it :)