L.M.
The Toys R Us stuff is expensive, like over $20 for each outfit. I'd try my luck at garage sales, Halloween clearance sales in November, etc. Also, Home Depot gives kids a free "tool man" smock if you go to a kid's event there. Kids his age are also very happy to dress up in their parents' clothes, to use pillow cases as capes, etc. Good Luck! And please report what you find, I'm in need of other new ideas, too :)