I'm looking for one myself. I was offered a 3" A. Maculatus for $65 but I'm kinda scared.
Seems they tend to not live long in captivity, several months at most, USUALLY. Some do live for years. Some never take to eating frozen or non-living food. They require very good water conditions. They change their color to suit their environment, so spending extra for a certain color isn't in your best interest. They enjoy hanging out around sponges.
I figure a lot of them probably die prematurely due to people overfeeding them for entertainment.
You should Google "Antennarius" and read about the different kinds. Like mentioned some grow pretty big, some stay relatively small.