Target and Babies R Us have plain colored t-shirts for $5 or $6
This fabric is from Hobby Lobby and I call it pockey dots (Though I have no idea what it is really called, I love to name fabric...weird, I know!)
I typed a #1 in word and found a great font and blew it up large and then traced it onto the fabric and fusible web
Iron the three layers together- top fabric, fusible web, t-shirt (Read directions, each brand is a little different)
Zig-zag stitch around to seal the deal and prevent fraying
And Voila... You are done!!