I'm not sure if this is a store only in the Northeast, but if you have a Chrismas Tree Shop they had them for really cheap. They also had matching umbrellas and boots.

i just got my 2 year old a rain coat on clearance at walmart for 3.00 they also had up to 5 year old sizes they were like a coat but light weight and can fold into a pouch if you can't find any on clearance look in the camping section or a camping store. i also got my oldest a spiderman poncho with sleaves rain coat at dollar general for $2.50.

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SILENCE IS GOLDEN BUT DUCK TAPE IS SILVER.

I was just on line browsing the kids dept at Macy and saw some really cute rain coats you might want to try there. www.macys.com

I bought both of my ds' rain coats off Ebay. They were in great used condition. In fact I think one of them was new with tags. It was $15 plus shipping