I got a Kindle brand one from Amazon that was listed for about $30 but I waited and got a really good deal on it(like around $10). Like this one:
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1 (mine is a regular Kindle, not a Paperwhite)
I got the kids covers on ebay for way cheaper. I think they are imposter kindle covers though...even though they say kindle on the front and look like the same design, they have cracked at the corners and broken. One of the sellers replaced it, but I'm tired of dealing with them and want to get the kids ones from Amazon...better customer service and probably a superior product(the one from Amazon hasn't broken yet).