there really is no cheap way, there is no aftermarket for a lumina Z34. not to mention your transmission can only handle 245 ft lb of torque. even getting close to that will destroy it. your best bet is to get a full tune up on your car, make sure your timing belt is still good, Z34s will kill timing belts around 60k. if you run it hard i would say a lot less. plugs and wires, get AC Delco and nothing else!
As for a little more horsepower, get a Cold air intake... these have to be custom fabricated for your car. not the cheap ones you see on ebay.. those actually make your car suck warm air!!!
go to
www.60degreev6.com or
www.w-body.com/forum
USE THE SEARCH FEATURE to avoid A$$holes that will chew you out for questions that have been answered sooo many times. 60degreev6 is your best bet, they go into detail on modding the 3.4 and other engines.
So for easy HP and some torque get a CAI (True cai not WAI)
and open up your exahust to 2.5 with a nice custom catback, dual of course, with a good resonator to help the sound, and some decent mufflers. I have flow masters on my lumina and i love the sound, also help on higher rpms to let the car breathe better.
Also horsepower for your lumina is as follows:
Automatic
200 HP 215 ft lbs torque (i think it is 215)
Manual
210 HP 215 ft lbs torque (i think it is 215)