Taxi Fare is normally 280 Dhs (300 inc. tip) Approx GBP 50.
I normally just book mine with the hotel and they just add it on to your room bill otherwise arrange it with the official taxi's in the arrival area.

Hiring a car is an option but after a 7 hrs flight can be a pain to have to drive and find your way etc. Especially if like me you like a bevvy in the air

I did once take a flight with Gulf Air DXB-AUH Flight GF603 IIRC. The hassle of going through the airport prior to departure / arrival and then having to still take a 20-30 min taxi ride to the city from AUH meant it was pointless. The flight was about 15 min alone, don't think the wheels went up.