1. for 200 you can get a nice barrell and some stickers, or you can get a good quality barrell that will shoot just as good (like a Lapco, or DYE aluminum or J&J) and have enuf to pick up some other stuff.
2. next I'd go with a KAPP or Shocktech(bomb) 3 way, actuating rod, Aluminum 45 frame(again KAPP, DYE or Shocktech are my personal fav's), and trigger plate, sear, and springs. Basically a whole trigger job from the grip frame down. You should be able to just get all this (#2 only) for around 200.
I reccomend these upgrades first because they make the most dramatic changes to the feel and performance of the gun.