[s346k]

1 e85. worth every penny when paired with other mods. typically good for 20-25 whp over 93 octane.

2 air intake system. it is my experience that any of the air intakes still utilizing the narrow factory bridge between the engine bay and front of the radiator will all suffer the same fate. ultimately being choked at the same place. this is the weird looking connection on the face of the rotofab air box. it's the same size as stock because it has to join a factory piece of the air intake system. removing the front of the stock air box will flow more than enough air for a mild bolt on car, and its free. LT2 manifold is 100% legit and worth it. 95 mm tb is not worth the hassle imho. the stock one flows plenty for mild bolt ons.

3 secondary cats. leave them alone. at best they make the car .2 db louder and offer 0 performance gain. as mentioned, removing the primary cats is the only way to get power from the stock exhaust system.

in conclusion, given your bang for the buck emphasis, my suggestion is as follows:

LT2 intake manifold
modified stock air box
flex fuel

spend the time & money on a quality tune. paramount.