One of my favorite sets. Been working on it for a couple years; very difficult set to accumulate in higher grades. The cards came in packs of 2 and 4, typically one of the cards has gum stains, which makes buying packs frustrating as at least one of the cards will be ruined (unless you don't mind). Miscuts, off-centered, bad coloring, and the general poor production process of the set mean NM-MINT + examples are fairly rare in some instances, and incredibly rare on some short prints (of which there are many). Even poor/fair short prints of common players command a decent price tag. Not sure if there is one, but I have never seen any GEM MINT card from the 1977 Topps Mexican set.

As for demand, I have seen some cards wallow on ebay for months; raw and graded. When short prints appear, they are quickly acquired in almost any grade. A couple key cards: