I know its a GEM 10 but

well then maybe $100 is ok but I just can't see buying a base card for $100 when you could get a couple Largent autos for that.

I agree and I wouldn't buy it but the older these cards get the less chance there is that another 10 will show up so it can only go up in value. Vintage collectors love gem mint vintage.
That seller is my bread and butter for graded cards :salut:

And I would pay ridiculous prices if necessary to obtain some random base cards that were graded.

If a PSA 9 or 10 1989 Score Gaston Green showed up i'd pay a good amount because I havent seen one yet. Set collectors will pay over :drunk: