You could always look at hotels in Luton or Bedford. The Hampton Luton Airport is right by Luton Airport Parkway station for example, and if you catch an EMT train you're into St Pancras very quickly! Most of the other Luton Airport hotels are a 10-15 minute walk, or short bus ride, while the Bedford and Luton hotels are generally a short-ish walk from the staiton. With a railcard, the price isn't too bad.