Okay, before you get confused by that link..."Blue Lobsters", in aquaria, are crawfish(or crayfish, or crawdads, mudbugs, etc etc so on and so forth). Blue lobsters, in the wild, or anywhere for that matter, are extremely rare.
I believe most species of blue crawfish max out around 6", they
will eat your fish if they can catch them, but most fish are too quick for the crawfish, unless they are sleeping. The ones at my
LFS are $20 US.
Maybe this link will help a little more.
http://www.bluecrayfish.com/