Well, there's always cheap flights to Prague. Yes, renowned for stag do's, but also a really beautiful city..try going through the week to avoid the majority of stag do's...how about Dubrovnik...again, good for couples to wander about and explore, cheap-ish..a bit different.
Thought of a city break in the UK? Being northern and somewhat biased, I would suggest hopping on a train and heading to any of Manchester (used to live there, amazing place, great shops, bars, etc), Leeds (ditto), Newcastle (where I live now - class, great sights, close to the coast, good bars and nightlife, galleries, restaurants, people). I just think that a lot of people from the south seem to think that the north is full of men in flat caps with whippets, outdoor loos and people on the dole....this most certainly is not the case, there's such great cities, countryside, coastline, people.....I DO sound biased, don't I??!
For my girlfriend's birthday, I'm booking either a nice cottage in Northumberland (maybe a bit far for you, especially if driving) or a nice, plush hotel in the countryside, close to the coast. You could do this in Norfolk or South Wales - great beaches, great countryside, bit of peace and quiet, and a bit closer to you than us Geordies! Hope this has given you some ideas.