It also costs around 100 euro for a new timing chain kit - so the garage is doing me no favours by charging me 500 euro for labour !
The kit is the least part of the job.
Replacing a timing belt or chain is a big job that can take hours and may involve a new water pump also (good practise to do this).
However, I too have never heard of a timing chain 'jumping'. It must've been seriously worn, maybe due to a lack of oil at some point caused excessive wear.
The timing chain is not really expected to be replaced at all. I had an old 1991 BMW with one and after 14 years, 120k miles and plenty of 'spirited' driving, was still in tip top condition, with just a tensioner needing replacement.
Is there a tensioner on Polos ? If it was removed, the chain 'could' theoretically jump I suppose....
Another point, if the chain jumped, and the engine started, there could be serious problems caused to valves, cam and possibly pistons as things are not in precisely the correct position and thing can collide. The timing chain ensures that the cam rotates at the correct time and therefore the valves open at the correct time and do not hit the rapidly approaching piston.
Any alteration in this timing can have serious consequences.