Quoted from SantaEatsCheese:Easy... There were 20 million people in California in 1970 vs 40 million today. The combined population of New Jersey and Pennsylvania in 1970 was 20 million vs 22 million today. ...
Thus ... more EM's available east of the Mississippi than west of it. And larger supply = cheaper prices.
That's why I transitioned from collecting EM's to just buying NIB games. Much less expensive!