So far in my Is250 i have installed:
K&N Typhoon intake
Lexus HKS exhaust

What else would be beneficial to help increase HP and sound?
I was thinking possibly a midpipe, but i dont know how much those run, and what they cost to install
Thanks!

 

PPE Headers, they run around $850. They sound great! and increase Horsepower as well.

 

Increase HP: Trade your car for a 350 or F. You cannot make a lot of power from these cars with mods. The cheapest (by far) hp/$$$ mod is trading up.

Sound: midpipes and headers.

 

^^
Yeah, if you're interested, you can probably focus more on making your car a better handling one with some suspension upgrades. It definitely changes the behavior of the car.

 

To answer your question, a mid pipe ($400) and headers ($800 for PPE) is the only things you can do and it'll only add about 12-15HP. The only other option is a supercharger (5K) after you get everything that's required.

 

...and even at that you're putting +50 at best.