Oh, you mean this one? Yeah, I bought it last August on eBay for $105.50. Honestly, I don't know for a fact that it's elephant ivory, but I have many examples of both mammoth and elephant ivory to compare it to, and to my admittedly amateur, untrained eye, it looks more like elephant than mammoth. It could be mammoth, I'm not claiming it's not, but it looks more like elephant to me when compared to other samples of both elephant and mammoth ivory.
At least you now know two things more than when you started this thread: 1) despite the rules, laws and what people want you to believe, ivory can be, currently is and in all likelihood will continue to be bought and sold on eBay all the time, albeit illegally, and, 2) the "value" of a similar knife to yours (remember: the true value of a knife is only the amount that someone is willing to pay for it, not what is printed in the so-called price guides.)
Welcome to AAPK!
Hope this helps.