There's plenty to see down in the South East as well for free or a reasonable fee, i'd recommend:
The Kent Battle of Britain Museum at Hawkinge on the sight of the former RAF BofB airfield
The nearby BofB memorial and 'Wing' experience at Capel le Ferne with a spectacular view out from the white cliffs
Manston's Spitfire and Hurricane museum and neighbouring RAF History Museum
Honourable mention to the de Havilland Museum in Hatfield, home of the Mosquito with three complete examples including the prototype.
If you can stretch to it, a tour of the Biggin Hill Heritage Hangar is excellent, the most (airworthy) Spitfires under one roof in the world I think...
There are quite a few other smaller museums and collections dotted around as well, Brenzett, Shoreham, Headcorn etc.
Fenrir and I are Kent residents, so feel free to drop us a DM if you require any assistance!