For fun go to ebay and look up 'Griffey Jr RC'. Your head will explode. All the different brands of RC's, (Topps, Fleer, Donruss, Score, Upper Deck, Bowman, to name a few), all of the different companies that graded his rookie cards (PSA, Beckett, GEM Elite, SGC, GMA etc.), there is no rhyme or reason to the prices. GEM MT 10 UPPER DECKS go for less than a GEM MINT 10 FLEER, but some go for more (I am guessing it may have to do with the grading company, much like comics?! ).
Meh...glad I ditched sports cards decades ago.