Noob shrimp questions

I have two questions:

1. Where is a good, and reputable, place to get shrimp online? I have found Shrimply Fintastic as well as Shrimp Up Aquatics. Are there any others I should look at?

2. Why does there seem to be such a large disparity in prices between different vendors? One place has shrimp for $3-$4 each and another place has the exact same species for like $10 each. Why is there such a disparity in price between vendors for the exact same species of shrimp?