there is a bread clip monopoly. Yep, Big Bread Clip exists and it affects us all. Its existence is not because of a strong patent position (the original patent having expired decades ago), but instead because the company making them, Kwik-Lok, is able to sell them at a price high enough to be nicely, but not excessively profitable. If Kwik-Lok were to suddenly try and gouge the customers, competition would soon follow.
Polystyrene (PS) appears to be the resin of choice, and that seems to be reasonable given the brittleness of them. Cheaper raw materials exist (any of the olefins for instance), but the cycle time for molding with PS makes it a winner. PS becomes almost watery when heated, so you can pump it into the molds very quickly and with little pressure, and when you have a bazillion clips to make every year, speed is essential.
Kwik-Lok is headquartered in the small town of Yakima, Washington. If you had nefarious intent and wanted to cause worldwide panic amongst consumers fearing that they could be facing a long-term future of stale bread, take out Yakima, Washington. And there's one man that is up to the task: