To me, the idea of being a student with a car in Manchester, is a bit of an unnecessary luxuary. You are living on one of the bussiest bus routes I've ever seen... you will not use a car to get around Manchester.
Maybe a car would be useful for some people when they do go home, but how often do you intend on going home? Factor in parking costs and your insurance for a year, road tax, petrol etc and compare that to however many return train tickets you think you're going to be needing.
There are times when a car might be useful. But to me at least these instances were not worth the hassle of my car being there 24/7. For the record, I had my car at uni for the last week I was up in Manchester. I went home on the train after my exams, came back in the car to party hard for a week or so and enjoy the end of term atmoshpere, then loaded my car with my room contents (it's a big car!) and set off for home.