Technique Tuning's (NickG) kit goes for $6800 (stg 1) for about 360rwhp, or $7700 (stg 2) for 380-420rwhp. This kit is pretty damn sweet but its for a m3
not sure what AAs kits go for but I think its similarly priced.
A guy named Techno550 (from racersmarket.net) on BF.C has a kit that comes with custom software and puts out impressive performance that I think goes for under $5000
Those are some of the more noteworthy competition imo, hope it helps