I've been looking around recently at the 3D Style rear spoiler for the e90 and I must say, it is the closest thing to a csl trunk that doesn't involve shelling out over 1k. However, the spoiler itself from 3D is pretty expensive and it doesn't seem like any vendor carries a rep for this.
Spoiler touched up in photoshop with no lines
spoiler touched up in photoshop from rear, looks pretty darn close to a csl trunk.
I'm sure if there's enough interest a vendor would be willing to make a rep for this. So if you like this spoiler and like to see it made, please vote yes!