A header +cat or testpipe will get you much bigger gains than cat-back exhaust. JDM 4-1, DC JDM 4-1 are some cheaper examples or you can go whole hog and get an SMSP, Toda, Spoon, et al if your planning a serious buildup with big cams. Otherwise the cheaper headers flow about as well on a mildly bumped up motor.

You don't say what year. If it's a 97-98 you can update to the 00+ ITR intake cam for a few additional relatively cheap horsepower, then sell the OEM cam and your cost will be maybe $100 (new cost - old sale).

Hondata Intake Manifold gasket ($60). Not a huge gain here, but insulates you intake manifold from heat soak which robs hp. It's something useful no matter what the build up of your car is.

V-AFC is useful, although it has no ignition control, so fuel and VTEC are all that you control. Useful, but not ideal. Hondata would be better, but more expensive. I think it's around $700 + tuning costs & dyno time. Not cheap, but if you do choose to go with big cams, it's almost a must have.

btw-if you've seen Trey's posts. He's running 13.8's at nearly 102 in a 98 ITR with basic bolt-ons (JDM 4-1, IceBox, Honda gasket, ATS FD). That's pretty d*mn good for a nearly stock motor on stock (00+ ITR intake) cams.