Refurbished second-hand bicycles can be purchased from Broken Spoke Bike Co-op, a community benefit society with charitable objectives. A bicycle trading marketplace is also available locally via Oxbike, and refurbished bikes can also be purchased via Rick's Cycles.
Alternatively, if you would like to donate your unwanted bike, please consider Broken Spoke or The Bike Project, which match donated bicycles with refugees in need of reliable personal mobility.
Renting a bike
Oxford is a great place with lots of options for renting a bike for the occasional ride or for long term hire. These include Bainton Bikes and Cycle.land.
Alternatively, use the Brompton Hire scheme to rent a folding bike from Oxford rail station.