I'm not from kansas... so i'll more my answer from the other thread, to this one...
catback (or other exhaust kit) ~$300-600
bigger throttle body ~$200
Headers ~$600
Upgraded PCM ~$250
optional accessory stuff - grounding wire upgrades, spark plugs and wires, port and polish (if you know a good engine guy)
If your looking for forced induction, try getting in contact with Blackjack. Hes building a monster 3.4L alero.
Abuse the search key, alot of the engine upgrades are commonly debated among members, as to whats good and whats not.
It becomes pretty apparent who the more knowledgeable people on site are. (i'm not saying myself... i can do general maintance and thats as far as my engine knowledge goes. i'm more electically/biologically oriented.)