Fully local (or private cloud sync) I would go as high as $2 a month. Cloud based solution, which is the only solution I expect, not interested just yet.
$0, unless maybe someone finds a way to not pillage the data of the service and add a lot of actual value, and doesn't squat on this ultimately simple thing that should be a small piece of a much larger thing.
open source AI and browser/OS companies are going to provide an answer soon anyway.
(note: not OP)