presume ur se has a zetec right? under that deal, what mods (if any) do u have...if none...then...
intake (iceman, volant etc) 200-250
catback (bosal, magnaflow, FS, apexi etc) 300-400
udp or set (AFX, esslinger, FC, etc) ~120
flexpipe (Bosal, FS, etc) ~110-130
cam sprockets (Kent, FC, fidanza, FR etc) 180-250
chip (diablo, Superchip etc) ~220
Port ur TB (free)
chop ur shifter (5spd) (free)
there r some other things u can do, but this is a good baseline. if u have an auto, then go after the chip as alot higher on list than if u have a 5psd which it can wait a lil. leave some bread aside 2 get the car tuned after all these mods (maybe wait til u've decided on any further exh work (high flow cat, ORP, shorty header or race header etc) then tune it.