I have a 53 plated A6 - as I recall (and mentioned earlier) they have a peculiar attachment to the arms - a sort of plug on and then push down a little clip. I may be wrong, but I think you will find that the "HOOK" type isn't the correct fitment, despite what the Bosch selector says - and indeed Halford's does as well. I know this becuae I bought a set of Bosch blades (from the seller mentioned earlier as it happens) and they didn't fit. We resolved it - eventually.
I seriously doubt you are going to find a cheepo set of replacements. I believe this is the fitting -
Valeo Audi | Euro Car Parts UKâs No.1 Car Parts Retailer
Also, check with your Audi dealer. They will of course be able to supply the correct blades. You might also be able to get a replacement rubber set - I know I did that in the past but I can't recall if the blades you have can have the rubber replaced.
I hope this helps you - Mike.