Most cars have risen in price but premium cars have seemed to have higher rises. You should still be able to get something decent for £20k though.
It is mostly the state of the market. To maximise your value look at the 3 Series - it is exactly the same car as the 4 Series but is the 4 door saloon version. The specification can vary inside, mind. But really now is about the worst time to buy a used BMW as there has ever been. You really get very little for your money.
Thank you both, what are the options that are a must?
I know Pro nav is the better option as you get the wider screen, auto gearbox, adaptive suspension, cruise control, heads up display. Anything else is a nice extra?