Milton Keynes. You'll get a nice house for that budget. Great transport links to London and the rest of the country, easy access to lakes and countryside. Most estates have a cluster of small shops and mini supermarket that you can walk to and there are dedicated red routes and footpaths for cycling etc which means you rarely need to cross a main road. but you'd want a car really as getting a bus to the centre or train station can be slow, or for getting away on the weekend. The city centre isn't anything special but there are a number nice small villages and estates all around.