You read that right, iam not looking for stockphoto's but stockvideo's

I ofcoarse found a few sites using google, but most are pretty expensive and since iam working on a non-profit video, i would like to get it cheap or for free.

Does anyone know quality free or cheap stockvideo's? Iam generally looking into nature loops such as skies, bubbles, flames, water, underwater, wind etc but all have to loop flawlesly.

An example (underwater):