Target had a sale on long sleeve t-shirts...$3.50 each. I bought a small and a large. I also bought a pack of boys underwear with a navy blue pair. Once I got home, I cut the sleeves off of the Large one and they became the legs for his costume. I took the blue underwear and sewed the shirt sleeves into them. Viola! Superhero pants.
Then I took the shirt and followed this tutorial to make the Super Why logo on the front of his shirt and to make a cape. Since I was already making the cape, I decided to make it reversible. One side is plain blue (which he needed for the costume) and the other side is red with a "Super J" emblem on it. I just made up the "Super J"...I know, I'm so creative. :)
The last thing I did was take some yellow ribbon and cut it to fit his waist. Then I burned the ends so they wouldn't ravel and sewed Velcro on them. This became his belt. And here is the finished product. Pretty cute, huh?