Price is definately for a pair - see Vines eBay add:
http://www.ebay.co.uk/itm/GENUINE-BM...-/160732617399
Most BMW accessories and Spares are covered by their warranty (see note in Vines advert above) - what will additionally be covered is your plastic lenses, bulb holders, wiring etc should there be any issues - some of these "higher performance bulbs" are hotter