A few years ago, you could get them for $25 - $100.
I researched for months (the reason I know so much) and was actually considering purchasing from a LFS that a friend owned and I worked at.
Went into work, one day and had my hands in a 24gal. nano cube, rearranging corals, when the new guy walked up to me.
Him: Hey, did you see the new octo I ordered?...it's in the tank your arms are in.
Me: Nope...didnt see it. Where is it? What species?
Him: Oh, I dont know the species, but it was really cool lookin...bright blue rings...there it is, right by your hand.
It took me about 2 seconds to look and see it less than a 3" - 4" from my hand. Yanked my hands out of the tank, almost knocked the whole tank over, controlled myself and didnt strangle the kid and upon closer examination, saw that the octo was dead.
He got the biggest butt chewing of his life, from me, about ordering things that he didnt the slightest idea about, etc.
IMO, unless you're in some type of research position, such as Dr. Roy (on -- and is a major player at Berkely Univ.) and are actually studying them for some accredited institute, they should be left in the ocean. Definately not an animal for lone hobbiests, no matter your experiance level.