A good start would be, as stated above:

1. intake (either CAI or if you wanted to save money to start, just a K&N drop in)
2. a new header (for the money, this can be one of the single biggest HP increases if you get a good one 2-15 HP sometimes)
3. cat. back exhaust ( I don't mean a fart can, I mean a good system. If you change your intake and your header then this completes that aspect.)

If you change the input, it makes sense that you should change the output; right? Doing what I listed above will get you on a good start where you're not forking out TONS of money to tear into the engine just yet, etc. Your car will breath better and flow better. You could get maybe like 3-15 HP just in doing those 3 things (and I'm being probably conservative, but I'm not going to go crazy and give big numbers because they simply won't be there.).

AEM makes good cold air intakes (CAI). There are others too, just don't do cheap.

DC Sports makes awesome exhaust components for Hondas. Specifically, the header.

Exhausts are all over the place. You've got guys like Greddy and Borla and lots of others though those 2 are pretty good stuffs.

There will be varying opinions. This is just mine and it WILL be a good start for the money and time invested. You might could do all of it for $1000-$1200 if you play our cards right. If ALL you have is the $600 for now, do an intake and the header first. You will NOT go wrong doing a header either way. Just do your research and get a good one, like a DC Sports.

Good luck.