They can both be purchased in the Travel Bureau in the foyer of the University Union building. For students staying for a while possibly the cheapest alternative in the long run is to buy a bike. Many Bristol students cycle to and from the University. A cheap, second-hand bike can be found by looking at the small adverts in newsagents or by buying trade newspapers. Bristol roads currently have a good number of cycle lanes.
Cycling can be a great deal faster than a car in the rush hour.