My wife's 97 1.0l polo has started having difficulties getting into reverse. Sometimes won't engage, and just grinds when the clutch is let out.

What causes this, is it expensive to fix??

The car has only 29k miles on clock so has been used for short journeys all its life, and is prob not worth more that

probably clutch drag , i.e. the clutch not clearing to allow the gearbox to stop rotating , its always worse on reverse and sometimes on first gear also , or could also be wear on the selectors in the box not pushing the gear across enough to select properly , just a few ideas , but it sounds like the box will need taking out to repair

Might be worth checking the cable is adjusting correctly.

How does the pedal feel? Stiff? Pedal boxes are quite common to fail meaning you get less effectiveness out of the pedal.