Hello Ken, 

For that sort of mileage it is a small bit less than you might normally be asked to pay for a diesel A3, but this would depend on whether it was a private sale or from a main dealer.

I'd say you would expect to pay €19,500 for one from a main dealer, with a private sale or independent dealer costing about €1,000 less. Remember, if you aren't trading in, you should expect you to get a decent discount off this asking price. 

Hope this helps!