There is an early more detailed thread on exactly this and more. These are made by Mann as you can see in the picture.
There is also a higher performance anti-allergen version of the filter from Mann available on Amazon for about $28 shipped.
The basic OEM version is about $18. That is IDENTICAL to the Audi or Porsche supplied unit other than missing an added part number. In fact Porsche got lazy and just added the Audi part number on my original.
Save your money and upgrade at the same time!