Sorry I can't help yo out specifically, but have you checked out the listings here: https://www.travelfish.org/accommodation/vietnam/hanoi_and_surrounds/hanoi/hanoi/all
I doubt many travellers stay over at Hanoi airport, hence the lack of replies. Someone mentioned Avi Airport Hotel in another blog I recall and it gets OK reviews on Agoda and is quite reasonably priced so might be worth a look. There aren't any other obvious options around there as far as I've noticed (no big Holiday Inns or anything!).