put me down for that too
As said before the cheapest areas to lok at would probably be Cowley and its a really short walk to the centre of Oxford so using a car would be pretty optional for that area. To be honest using a car in Oxford is pretty pointless, most places are easily within walking distance and there is always buses or a bike but if your going back and forth to Northampton it might come in handy
If your thinking of going a little bit farther you could try having a look at Headington? straight drive into the centre too.
I would definitely look at staying in uni accommodation for your first year though, its a great experience, everyone is in the same position and you'll get to know the area well enabling to decide either if you want to commute or where to live for your remaining years of study.