Not sure if it meets your requiremnt but Oxford (sorry, London Oxford) is a proper commercial airport although no scheduled traffic (I tell a lie, one a week in the summer, I think) and not too expensive. I did some T&G there in a PA28 recently for less than a tenner each. That's a weekend rate, it's more expensive Monday to Friday.
Gloucester already mentioned is big and busy for a GA pilot but very do-able, it was of the points on my QXC earlier this year.