What a bummer...
Well the trunks are all very different and depends on the look you're going for. I'm gonna guess $500 to paint the trunk and $75 for install if not DIY. There have been many in the for sale section of the forum, check it out.
2011.5 Jet Black E92 ///
M3: ZCP|6MT|BB|DINAN|EVOLVE|BPM|VORSTEINER|BMW PERFORMANCE|IND