There is an ATM that is very obvious in the arrivals/luggage hall, after you've gone through immigration checks (but before customs)

I've done this trip numerous times with long overnight layovers, rather than hanging around the airport/expensive airport hotel, but you do need cash. You can use Uber for the return fare. I forget the exact amount of money I paid, was it about 80QAR to the nearer hotels and the furthest away (Ritz Carlton) was maybe 100QAR - so get a bit more than that to avoid problems. I then used uber to return back from the hotel to the airport using their wifi. [Edit, this includes the night surcharge just to clarify the prices, the websites say that it is cheaper at about 40-50QAR, but I'm always arriving late at night]

The taxis are really well organised and it isn't worth the hassle of uber when there are always cabs waiting and very well organised, for the same price.