you won't find elephant ivory as it's been a controlled substance for many decades now. Any still out there is that old, and priced accordingly. (close to 1000 for a set of panels)
Mastadon ivory is around and a bit cheaper, somewhere between half and a third this price
What your can get is a few different varieties of horn/antler that look very similar, or polished bone...of these, the bone is the cheapest, and looks good. There are several makers of faux ivory, some is very good, some is poor, check the reviews.
hope some of that helps