Second of all if you can't push the costs high enough then it becomes time to limit the cash budget of state level actors. Which is hardly without precedent.
For some reason you seem to only be looking at this as a technology problem, while at the core it is far more political. Sure technology might help, but that's the raison d'etre of technology.
I doubt they made a deal that didn’t directly served either Israeli or US foreign policy and security interest.
I don’t know about the NSO but another player in mobile tracking (Verint) tho very much more LEO oriented (SS7 tracking) had about a million failsafes that ensure that their software cannot be used to track or intercept US or Israeli numbers.
Currently, some blackhat somewhere finds a vulnerability and sells it to NSO and then NSO sells it to various countries. If Israel forbids such deals, then the same "someone's" (without regard of where they're located - those deals are essentially unregulatable, you might anonymously trade knowledge/PoC for crypto) will sell the vulnerability to NSOv2 headquartered in Panama or Mozambique, and NSOv2 will sell it to the same customers.