why oem? most of the good brand aftermarket stuff is so much better than the vag oem
for example, the spring/damper combination is far too hard/crashy right across the range - a simple setup like koni fsd dampers with eibach -30mm springs is a million times better in terms of ride quality and road holding/handling.
the biggest oem ARB is too small, particularly for the rear, although the r32 front bar at about 24mm isnt bad if you pair it with a 24 or 25mm rear from neuspeed
best ARBS that suit the a3 are either Hoskiss or the Neuspeed but neither is cheap, but they have the increased rear stiffness that reduces the understeer considerably
having said that, a full set of r32/s3/3.2 345mm front and rear oem brakes can be had for about£350-£400 and are brilliant for road use compared to the 280 or 312mm front set up.