Dudes, the whole point of his question is that he doesn't have blower-level money. Cams, ported heads, a full LT exhaust? That's the $5k right there that he says he doesn't have.
To the OP:
1) jump to a 93 octane tune, there's a bit more the be had.
2) Ford Racing intake plenum and throttle body (roughly $800 if you do your own labor). will go well with your CAI, and opens up the top end a bunch. Plays really nice with better cams or heads should you go that route when you do have that kind of cash to play with.
3) GEARS! It will make your car feel a lot more powerful, shouldn't cost more than $400 at a local shop, and it doesn't involve messing with your motor. If you are running factory cogs and you jump up to a 3.73 or a 4.10, you will definitely notice the car pulling a ton stronger.
4) high-flow midpipe and a catback. This can make your car sound better, you can do it piece by piece because if it's all stock style it all works together (IE- midpipe now, catback after that), and it will help you pick up some oomph. LTs really won't be worth the hassle unless you go crazy on the motor or put a blower on it, and with LTs you have no choice but to at least do headers and a midpipe in one shot.
5) full
suspension kit. yeah, I know it's not horsepower, but if you can put down and keep down all the power you have now, your car will feel faster. Roughly $1200 for a complete kit from a company like Roush, and being able to lay down up to a 1G lateral turn will really allow you to carry the power through turns around town.
6) better tires/rims. Again, better handling allows you to maintain your pace and keep more power planted. It can either compensate for your stock
suspension, or complement an aftermarket one by really holding the pavement. Less wheel hop=better acceleration. Better grip=more speed with lateral G loads (on/off ramps etc.)
You aren't going to see 400HP to the wheels without getting into the previously suggested heads/cams/intake/long tube setup or some kind of forced induction on a 4.6L motor. That's 5.0 Coyote power, and without some serious modding to a 4.6 to level off all of the advancements, it's just not reasonable to expect that kind of output from the 3V. Sometimes beefing up the stuff around a motor can make the car feel like it has more power because you are able to efficiently harness all of what you have. Good luck, and keep in mind that once you hit that 400HP mark, 500 is going to be waiting there, daring you to chase it down.