There is no simple or inexpensive way to increase hp on a camry. Inexpensive: what's you budget and what do you consider inexpensive? Simple: Are you looking for complete bolt-ons? --> Good luck cause they're few and tend to be expensive.
If you're new to the Camry scene then try these:
Ram Air Intake or Custom Cold Air Intake (WeaponR avail. for V6)
Performance Muffler --> remember: what you pay is what you get (usually)
If you have the 5sfe then get the RippMods header (you might still me able to get in on GB)
Redo/upgrade everything from headers to the muffler
Work on the ignition/electrical system --> might not necessarily increase horsepower, but it'll get the car running smoother and more efficient.
AND YES --> A turbo or supercharger is the best way to go for more horse power.
There are a few examples on turbocharged and supercharged camrys. Check what they have under the hood cause they're bound to have something that increases hp!
and kill your engine without those forged internals. Plus you'd need to bore your engine to fit in the 3SGTE application pistons then connecting you'll need connecting rods. Then SAFC and on and on and on and on....
it will never be inexpensive...you can always get a short ram intake or cold air intake made by injen which will increase the ponies by 2-3 for roughly 200 bucks...then exhaust headers if you can find them try jpperformancellc.com and or call them you are looking from anywhere from 300-500... then exhaust muffler and as the guy said b4 you get what you pay for....there is never anything inexpensive but it's reasonable....another thing is to get a power enterprise camcon which helps your valve timing that can give around 15-20 hp if you know exactly how to set it up and that runs around 380-400