Well having tried it for over a year at OAT, no it isn't excessive! However it isn't the tightest budget you can imagine - rent and food bills (80 quid a month) come to 400, my life insurance, loss of licence insurance, and mobile bill cost me another 100 quid a month, leaving me 500 a month. Car (petrol) costs me say 80 quid a month, 400 quid a month, 60 quid off the credit card a month (trying to pay the bugger off!) then around 75 quid a week to use for my own use...and having been a student for 5 years now, that allows me to live more like a grown up and gives me chance to go out for some light socialising and do the things that you can't afford to do when you're on a shoestring...and most of the guys I know here don't want to have to live on a shoestring because it's a bloody hard slog!
Having said that, if you can live off 250 quid a month, good luck to you...but it won't be easy and you won't have any margin for relaxing which as anyone who has done this will tell you is heartbreaking when your mates are out 'socialising' on friday after being in groundschool all week, or when they go for a trip somewhere and you have to decline...