I second teh ebay thing. My son was a ring bearer, and I found a really cute and CHEAP suit, that worked great. as he was only going to ever wear it once. I think I paid something around $35.
Best quality boys formal wear is at CandyGirlDress dot com. Made in Korea, not China like eBay sellers. Fabric is different, finish, and craftsmanship can not be compared to Made In China Tuxedos on eBay.
Plus CandyGirlDress dot com, boys formal wear is on sale at $45, and if you enter promo code "A8792777" you will be able to steal for $36. A dollar more than eBay. But the quality is very very good.
Plus consider ordering dresses, they have hundreds of flower girl dresses. And if you combine an order $120 or more shipping is free.