cheap upgrades.
go to muffler shop have them replace your resonator w/ straight pipe.
take off your exhaust manifold and port out the collector along w/ the downpipe a touch.
take off your intake manifold and dremel off the "de-tuner lip" on it to gain a slight gain.
swap out your crank pulley w/ the older 2.3L LGO crank pulley. smaller in diameter and lighter.
buy an 2.4L intake for a cavalier on ebay.. less than $70 and usually copycat designs of the popular ones made by RSM/RKSPORT/AEM/INJEN
OBX probably makes a lightweight crank pulley for less than $100
if you're really good w/ working on motors. find a junkyard w/ a 1995 quad4 2.3L powered car, take the intake cam, and than find an older LD2 from 1990-1994 and steal the exhaust cam. Buy some fresh gaskets and swap them into your 2.4L. That's actually a cheap upgrade albeit labor intensive.
also take a 2.3 56mm throttle body sensors on it too mind you, with some work it can be modified in your garage to fit on a 2.4L intake manifold. How do I know? Look at the throttle body sitting on my 2.4L intake manifold right now. *that's right I"m not sporting the 2.3HO manifold anymore, not enough velocity in my opinion*.
Go buy an 02 simulator from casper's electronics and have an exhaust shop remove your cat and replace w/ straight pipe...
CHEAP UPGRADES