Well I live in East Anglia, I enjoy days out and I've got a birthday coming up, So I've booked a day trip to Paris (with no driving):
2 x taxis to/from station = approx £25.
Trains to/from London, which is about 75 miles away (with Advance tickets) = approx £24.
Return fare to Paris on Eurostar (at offer prices) = £58.
So that's one possibility. If your father can get to Stansted, there are also loads of cheap day trips available from there, such as Amsterdam or Berlin.