You're right they have went up in place.
These were the ones that I have on my car, got them in January of 2012 for about $215 for the set.
E53 x5 1999 2006 LED Tail Rear Light Red Clear for BMW V1 | eBay
Just a quick check on ebay and the red/clear and red/smoke are $300 or so.
The black/clear ones which look so aftermarket still hover around $200, prob because they don't sell as well. These lighting distributors tend to test the market with higher prices if one style sells better than another (Depo E53 headlights comes to mind), as long as people pay the higher prices they will stay that way.