I took last Friday off work, and took the Eurostar to Paris for a long weekend. It's a little over 2 hours on the Eurostar from Kings Cross, so its really easy to go to for short breaks. You might think it'd be super expensive for a weekend away in Europe, but really you can do the trip on a budget and still have a great time.
Firstly, Eurostar tickets - on the day i think these are over £200 return, but book in advance and your tickets can cost as little as £59 return. I paid £65 return - but I could have gone for the cheaper option, the train time just wasn't as good for me. Top tips: Eurostar sells youth tickets - so if you're 26 or under, check those out. Eurostar have Sales a few times a year, they're on Sale right now, but you can also sign up for Sale alerts so that you never miss out on a good deal!
Secondly, accommodation - I did look up hostels, but found them to be quite expensive in Paris, unless you're staying in a huge dorm room. I wouldn't usually mind a hostel stay, but as this was for more of a relaxing weekend away I decided a Hotel would be better suited.
I found a great deal on a Hotel in the Gare du Nord area (ideal for Eurostar) which worked out to be about £30 a night each (based on 2 sharing) which was actually cheaper than a lot of the hostels I'd looked at. The exact hotel I stayed in was the Kyriad Hotel in Gare du Nord, details here: http://www.kyriad.com/en/france/paris-region/hotels-paris. A basic hotel, but very clean, comfortable beds, great staff and a modern bathroom.
In terms of eating and drinking out, I'd say Paris is similar in price to London. As expected in any City with good tourism, if you go to a restaurant near a big attraction you'll be paying over the odds. Simply walk a few streets out, and you'll save at least 1/3 on your bill if not more.
I was so lucky with the weather - Saturday was really mild, light jacket weather rather than full on Winter warmers so I didn't have to spend a fortune hiding out in cafes, instead I had the pleasure of wandering the City and seeing the beautiful sights.