According to Wikipedia, one penny weighs 2.35 grams
2.35 grams * 52 662 = 123.7557 kilograms
That is 272.8 pounds of pennies! Postal rates must be lower than I thought if he can mail 270+ pounds for just $50. I even tried the online postage calculator on the USPS website. When I entered 273 pounds, I got an error message that it exceeds the 70 pound limit.
That thought struck me too, (about the weight of the pennies), I've mailed heavy packages before and it's not cheap. I never have mailed anything that weighed as much as 70 lbs and didn't know about that limit.
Would be good to know how much to send 4 separate packages.