There are loads of hotels within a taxi ride of the airport. On site as has been stated is a Hilton (not cheap), There is also a Welcome Lodge at the service area that a lot of my clients use which is at the junction of the M11 only 5 mins from the terminal. Thats £75 RO
per room. A little further away is Briggens House at Stanstead Abbotts, Moat House and The Green Man at Harlow. Or like Pe@rson stated travel in to London and stay at the hostels or even the Imperial Hotel on Russell Square. A Twin/Double is only £92 B&B or a single room is £73 at Imperial or its sister hotel the President is £69 B&B
If you require any further help, let me know.