Welcome to the mad house Jamesy!
I'll be blunt as it's the easiest way, I recently bought a 2007 civic 1.8 vtec as my daily driver and I'm looking for a weekend beater! The reason it's my unmodded daily driver is that you are limited with what you can do with a naturally aspirated engine, somewhat especially the vtec.
For the money you are spending I would agree with Prince I would look at a decent exhaust system maybe even get a custom build if there is someone your side of the water that is decent.
In terms of air intake personally I would avoid the Induction kit's and stick to a good panel filter to help the car breathe. Reason being the induction kit will give more power but generally only as the engine gets to the higher rev range. Fine on a normal car but a vtec you can rev the nuts out of it. In other words you may spend a couple of hundred for a lot of noise but no go.
This will most likely chew a good chunk of your budget, if you do perform a small miracle and get all this cheap then maybe look at brakes. (I have just horrified the entire forum) This is more for a style point of view as you will give the car a better look with grooved discs which in turn mean you can brake later meaning you can go faster for longer and most insurers won't put up the premium, some may even reduce it? Style, function and safety all for a couple of hundred quid!
Beyond that you are then into the realms of spoon parts, custom ecu's, fuel rails, injectors, clutch, flywheel etc which to go back to my original point wont have as big a gain on a naturally aspirated engine so again a lot of brick but not much kick.
Overall though I would do these three mods and then set yourself a goal to get a project car.
I hope this helps and Waynne if this doesn't get post of the month then I'll be very dissappointed!! lol
cheers