I just purchased a child sized white lab coat and black bow tie for my ds, 6. He is going as a 'mad scientist' but I don't say the 'mad' to him, he thinks that means 'angry' scientist.

Anyway, I am embarrassed on how much it cost, the coat was $27 with shipping (those darn shipping charges always get me) and the bow tie was on $5 but with $8 shipping! It's insane!
But, I have to say that this is his 6th Halloween, and all the other costumes were very very inexpensive, and he's Hard to shop for. I won't do anything gory or really scary, and he's not into characters at ALL. Last year he went as a cowboy, and although he looked great it was not his personality at all.
So now that he's old enough to have some major input, I suggested a scientist and he Loved the idea! So like I said, he's wearing a child sized lab coat, a black bow tie, I'm going to buy him black jeans (he can wear these later too), and he'll wear black tie shoes. Then we'll replace his glasses with crazy round ones, spike his hair up, pin a rubber rat onto his shoulder, and pin on a test tube filled with green liquid (white glue mixed with green food coloring) onto his jacket. Add a pocket protector and a pen, and he'll be all set!!
I love Halloween!!