It's a fair price, just about right. If good condition and no cracks (hold the chip between your eye and a light bulb, and tilt chip a lot looking for crack or light coming through) could be worth a little more than $20 each. These ivory chips are coded for virtually every little line difference, and I am not going to check them against the book, etc -- but they look rather common to me. All ivory chips in good condition, have value, though. Congrats on your first ivory chips.

My best ivory chip is pictured below. It is exactly 2" diameter. At one time it was considered the largest ivory chip known, diameter-wise.
Robert