Chip board letters are super cheap ($1 each, or even less if on sale). They make for great crafts because you can keep your cost down.
I made this cute sign last year. I simply painted the letters green, then coated the front of them with modpodge and gilltered them. I then beveled a slit in a board thick enough to support them and hot glued them in/on. The shamrock in between the words is a nice touch to break it up and add the dimension of another color.
I am so happy with how it turned out. Total cost <$8.