If you want a cheap ting try the FSE power valve on the 16i, will make a bit of a difference, It replaces the fuel pressure regulator and basically enriches the mixture a bit [depending on the setting] and allows you to run a higher fuel pressure on acceleration, but normal on constant load so you're not caning your petrol

I've had a few injected cars with these on, a nissan 100nx, honda civic vti etc and it made a noticeable difference considering the cost was about £80

Other than that, see above you gotta sort your breathing out before doing any other mods, so look for a decent 2nd hand exhaust and direct induction kit

Next move would be a decent cam etc, but whilst they're doing that you could get a head skim and lighten and balance the flywheel??