We don't expect to pay local route taxi fares. We typically offer, for the two of us, $5 for travel within the beach area OR West End and $10 for travel between the beach and the West End. Rarely have we been turned down. It may cost you more if it's late and not many other taxi's around.
Although taxi's in the states can cost a lot more and Negril taxi's are much cheaper, I'm finding that with Uber or Lift the rates are comparable to what I've been offering above in Negril.