Hello Imram,
I wouldn’t be treating this critical application work as a ‘best price quote is king’ job.
My rule of thumb is change at 75K or 5 years whichever comes first.
The quality of parts is critical in my book, and I would suggest limiting your brand choice to Gates or Dayco, if not buying from Audi - you will probably find Gates belts in the Audi box even if you do.
Water pump ( if cambelt driven on this engine):- You will encouragingly get healthy and varied opinion on here - which is always good. Mine, for what it’s worth, is that I would stick with an Audi pump for a little more, rather than using the bit cheaper route of buying Gates or Dayco kits which include the water pump - based on previous experience of premature pump failure coupled with same experience on a non-Audi earlier this year.
Best advice I can give is do your own research and make your own decision.
Renewing auxiliary belt and assembly at the same time is very sound advice.
Cost? Easily costed at nearest Audi, but worth shopping around other dealers a bit further afield, since some do/did special offers from time to time. Personal opinion - if they have a deal that includes a free MOT during your ownership - avoid like the plague. They will have your discount back off you in record time!
Try recommended independents in your area.
Try your trusted local garage, but discuss parts to be used before agreeing to use this route.
Good luck with it, and perhaps you could let us know how you get on.
Kind regards,
Gareth.