Tbh this depends entirely on where you're studying and the kind of people you're friends with. I knew people who spent their entire budget for the term within a couple of weeks, but that was in London at a uni with a definite reputation for non-stop partying. Not drinking will definitely save you money, and in a lot of cases the novelty of being able to go out to bars and clubs wears out within a couple of months and other people will be more inclined to have quiet evenings in, so there'll be far less pressure on you.
In all honesty, people who judge you for not drinking aren't worth being around in the first place.
The best way to figure out a budget is to find out how much it costs for soft drinks etc at the student union, pubs and bars around your uni, and go from there. You'll probably find you're spending more on food - people get tired of cooking their own stuff really quickly!