I would agree and take Don's words seriously. You may be able to hunt for one at a cheaper price..... however, his price should be a good guide/reference point.
In my opinion, two most challenging series to collect are: Chinese Panda (early/pre-2000 date) and Mexican Libertad (fractional, 2oz, 5oz, and proofs). The reason is because of the varying mintage year-over-year. The market for Libertad is still small (compare to Panda) but the mintage for some of the Libertad is TINY.
Btw, Don should have a list of the mintage of ALL Libertad. You should look it up.