So many options in Europe if you don't mind discomfort. From the UK, I'd maybe take a cheap flight to Poland or even the long distance bus. Once there, YHA hostels, camping etc.

Another option is fly to Greece and island hop on the ferries. Or Portugal and northern Spain. Buses are the cheapest way to get around there and fairly flexible although not quick. Sometimes you can hire a car for a week for $250, or some places hire mopeds for way less.