I bought the Thule bars.
This is the list for my A3 (I DO NOT HAVE A SPORTBACK so check on the sites mentioned above to see if there are any minor differences).
At least this gives you an idea of what to look for.
Aero Bars ref 869 (or standard bars ref 769)
Foot pack ref 750
Fitting Kit ref 1314
You should be able to get all of this for about £115 (or £90 for standard bars).
I also bought 2x cycle carriers ProRide 591 and a one-key system upgrade.