The Rodent Crate costs 2000 commissions. But what does it actually do? The tooltip doesn't specify.
Using it will spawn Sumprush Rodents for one hour that can be battled and captured by anyone wandering by. Like other battle pets, they have a chance to be rare when you engage them.
The crate is the only way to get this particular pet. If you haven't heard of these beaver-like rats, that may be because they are not part of the Pandaria Safari achievement. They have different abilities and colors than the similar Bucktooth Flapper from Jade Forest.
Be sure to tell your friends when you're releasing the rodents so everyone can get one. The actual crate is so cute and weird when you place it down, I hope it becomes a Toybox item someday.