I think this is possible with a Grand Taxi from the airport. As far as I'm aware, the "official" price on the panel at the head of the taxi rank is 650 dirhams to El Jadida (although I pay considerably less as I have a regular taxi driver to take me there). From El Jadida to Oualidia is 150 dirhams in a Grand Taxi, so together, it shouldn't be more than 700 as a direct journey, although if you insist on the motorway, you will have to pay the tolls on top. I have an idea that there is an official price on the panel for Oualidia but I can't swear to this.
Please ask at the airport information desk for up-to-date fares to Oualidia. The taxi drivers often try to say the panel prices are out-of-date, so don't go over the information desk/panel price.
As a matter of interest, what was the price quoted by the hotel?