Abu Dhabi airport provides sleeping pods for rent, It charges 45 AED / hour (1 USD = 3.65 AED). Pod is a chair facility which could easily converted into a flat bed. If so it is gonna cost you like 75 USD for 6 hours renting. While (according to
booking.com) the airport hotel premiere inn offers one double room for 70 USD / night. So I believe you better book a one night room at the airport hotel for best value of money specially it is a walking distance from airport terminal.
While you also could seek an
Abu Dhabi layover tour from the airport to discover around the city instead of spending transit time just sleeping! and then sleep as much as you love at the connecting flight!