Fenbendazole works the same way as chemo drugs like the taxanes and vinca- derived drugs by preventing cell division. Right now it's affordable from Amazon, where the Merck product is sold for dogs - I just paid $16.67 for a month's supply (12 packets).
But a related drug, mebendazole, a WHO "essential medicine", now (according to Wikipedia), costs $440.00 in the U.S. because an American generic drug company bought the (U.S) rights from Teva in 2016 and hiked the price astronomically - it had been $18 a dose in the U.S. This for a drug that costs 4¢ per dose in the developing world and $5 in the UK and Australia.
I can only hope that Merck doesn't sell the fenbendazole rights to this blood-sucking company. They're another Valeant or Turing (of Martin Shkreli notoriety). I feel like I should maybe buy a lifetime supply now. With so many domestic animals besides humans needing deworming, maybe it's safe as a veterinary drug for now. But if research proves irrefutably its cancer-fighting potential, look out.