Woodchopper I believe they say you should change your disposables by length of use as well as mileage. The fact that she is only doing 3000 miles/year probably means she is a pensioner on a fixed income so maybe �24 is half her pension. Also the non avilabability means she has to travel a great distance to purchase the item.
Honest Joe - If its not in use it wont get clogged - keeping a partially clogged air filter in will only increase the fuel consumption - as for travelling a great distance - how do you know he/she doesn't live next doot to Halfords - a bit of give and take me thinks - at the end, it is up to them to decide.