The OE supplier is probably Mann, so the OEM filter from the Audi dealer will probably say Mann on it.
Mann, Mahle, and Hengst are the best cartridge filters to use for your Audi, since the OE supplier is almost always one of those three.
There is an eBay listing for four Hengst cartridges for $36, so $9 each. The Hengst part number is E32H