What prevents a farmer from simply switching back to the non-GMO seeds if the GMO option goes up in price? Or even ignoring that, switching to a different cheaper GMO seed from a different company?

I think that's the piece I and others are missing, isn't it ultimately a question of which seeds will make the farmer the most money? If a particular GMO seed suddenly become so expensive that either non-GMO or other GMO seeds are more cost-effective, why can't they just start using them instead?