for zetec mods on a budget, i found the decat the best bang for the buck. had to put a cat on my old (standard-ish) 2.0 zetec mondy for the MOT and it felt so much slower compared to with no cat!

induction kit makes it a bit quicker at mid-high revs but at the expense of power lower down (can make it feel sluggish around town).

another cheap easy power upgrade to do is underdrive pulley.

lightened fly helps alot on the zetec too.