I am actually surprised at how long it took to sell out.
I think it's only a matter of time until bigger companies start to capitalize on the second hand market. In this case, the game being re-issued is one of the most common and cheap originals, and it still found an audience, so imagine the money to be made when companies start re-releasing games that are fetching high prices, either due to scarcity or demand.
With that said, I wouldn't even pay $10 to add this cartridge to my curated collection, let alone ten times that. But if Sega were to re-release Elemental Master (given they own the IP), or Capcom the original Mega Man for say, $50 MSRP, I would definitely consider it.