See https://taxis.eservices-comstbarth.fr/sbh_taxi.html

If you click on Grille des Tarifs it will give you the rates. Taxi from the Ferry to Saline is €25 each way. Taxi from the airport to Saline is €20 each way.

There's also an app, but I don't know what cell service is like around Saline these days. If I were Taxiing, I would arrange a return pickup time just to be safe.
http://taxistbarthsapp.com/

If you choose to rent a car, there are two local agencies which I highly recommend. One is Gumbs Car Rental http://gumbs-car-rental.com/ and the other is top-loc http://www.toplocstbarth.com/
Both are locally owned, with excellent reputations. Both will rent at the harbor if that is yoiur preference. Depending on when you're gong, their prices may be higher than what you've already found.