Your have 3 choices when it comes to buying a bicycle.....
Buy a new bike. If you are a member of staff at the University of Birmingham and you meet the criteria, then you should look first of all at the University's salary sacrifice cycle purchase scheme (in association with Cycle Solutions (birmingham.ac.uk). This will save you up to 40% on the cost of a new bike.
Buy a second hand bike. There are a few shops that sell second hand bikes and the West Midlands Police auction off unclaimed cycles periodically.
Hire or borrow a bike. This gives you a chance to try out different types of bike (road, hybrid, mountain, folding, recumbent, power-assisted etc) before deciding what to buy.