Bruges is indeed a lovely city but it might be better to wait until the summer (or at least the spring) to visit it. That's because it's an excellent base for visiting the Belgian coast (with Oostende about a quarter an hour away by train, and several other resorts easily accessible).
Amsterdam is a lovely, compact city, which has great bars and restaurants, as well as loads of things to do and see. (Cat lovers will find a museum dedicated to them!).
It might be worth checking out the prices of flights to Barcelona's three airports, which are often really cheap because there's so much competition. (BA, Jet2, easyJet and Ryanair all fly to the wonderfully-named El Prat airport. Ryanair fly to Reus and Girona, but from only a few UK airports during the winter). Barcelona is a fantastic city for sightseeing, restaurants, bars, etc.
Paris is a possibility but it might depend where you're stating from. (Eurostar return fares start from £69 from St Pancras, Ebbsfleet or Ashford. Booking on the Eurostar website, rather than buying separate tickets, allows you to travel from many other parts of the UK for around £89).
Another suggestion that comes to mind is Bordeaux. It's an elegant, refined city, with stunning architecture and a great deal to recommend it. Being in the southern part of France, the weather will probably be far better in late February than in places like Prague (where temperatures often don't rise much above freezing, if all).
If you'll will be booking travel and accommodation separately, he should take a look at this website for cheap accommodation:
http://www.hostelworld.com/
(Don't be put off by the word 'hostel' in the title. Simply enter your dates and destination and start your search. You can then use the filters to remove 'hostels' but to retain 'B&B's' and 'Hotels'). I've found excellent accommodation from that website, such as a good quality central hotel in Madrid (which is another possibility, BTW, if you can find cheap flights), with air-con and free wi-fi, in peak season for €32 per night.