Man is that ever a loaded question. For BMW's you can get all sorts of mods. From reall cheap off shore generic "you make it fit" to good German or North American stuff. It really depends on where he want's to go. I would assume that if he spent the money on a 2002 325I, he probably won't scrimp on mods. They are sites line:
http://www.dinanbmw.com/
http://www.activeautowerke.com/
http://www.turnermotorsports.com/
Just to name a few.......Hope this helps.