I second what tom tulpe said.
The strip of motels along Great Eastern Highway, between the airport and the city centre, are the closest. None of them are upmarket, but would be fine for a few hours sleeping. Do double check that they have 24hr reception, given your late arrival. You can easily check them out on google maps.
The airport is quite close to the city centre, so going to one of the more upmarket hotels there is feasible.