Well considering the regular red firefish can be had for a whopping $12 at my LFS I'd say you could safely get double that! lol I'm sorry I actually have no idea. But maybe the [HASHTAG]#reefsquad[/HASHTAG] will know!
From what I've seen with firefish, despite some conjecture of it being a genetic aberration from birth, I've seen it occur from an injury to the dorsal spine, and instead of healing as it should, it heals as two separate spines.
It is an interesting growth form and doesn't occur frequently. It's value is relative to what someone will pay for it. At the end of the day it's still a firefish.
I have no clue, it should be pretty awesome to have one but what ever the hobbyist will pay for it.
Some hobbyist are ready to pay anything to put them in the picture of attention.
I remember the no tail Bandit Angel that went for a good dime.