Speak to Teddy at SSDD Motorsport (on holiday until end of Jan). I bought the units off him for £25 and they've never let me down. Looks the part too. I'm sure you can also change bulbs, but as I changed the units, it was about a 10 second job, if that!
Alternatively, have a search on ebay for the units and you might be able to get them cheaper?!
Also, see this thread.. http://www.e90post.com/forums/showth...r+plate+lights