A "fair" price is largely subjective and of course if you're the buyer you want it as cheaply as possible!
USD$120/pair is OK I guess if money is not an issue (add another 30%+ for CAD$
) USD$60 a pup is certainly cheaper than the $150-180 asking prices on the rest of that eBay page.
There was a time when you could find these pups at around $40-50/pair on eBay, and even cheaper in places like Kijiji and Craig's List. But as we've commented many times before both on this site and in the Westone Forums, "the word is out" on the quality of the MMK line of pups, the 45's in particular, and the prices continue to go higher.
The best answer is, "whatever you can afford" depending on how badly you need/want it.