Girona10 is a special initiative taking place on January 14/15 with all sorts of discounts and events, which look pretty tempting to me.
From 11pm UK time tonight (Jan 3), there will be 1000 hotel rooms available for €10 for Saturday, January 14. You can book directly on the hotel websites, or through booking engines.
There will also be set menus on offer at 50 restaurants for €10, as well as free entry to museums and discounts all over the city.
Shops are going to stay open till 10pm, so it should be a lively evening what with one thing and another.
More information here – not in English yet but the list of participating places is self-explanatory.