Budget 5.3 build
 

Hey guys I'm new to this but I have a 2001 silverado with a 5.3 stock besides a CAI and flowmaster super 10. Looking to get some power (about 400hp) as cheap as I can. I looked into turbos and superchargers but I'm afraid it's gonna tear up my motor since I have 273K miles. Any ideas?

a cam swap will get you there easy replace oil pump and cam chain while down there

What cam would get me there? And will I need new heads? Or have the stock ones redone?

Those heads you have now will exceed your goal. For 140 bucks you can slide in a LS9 cam and make 420 horse at crank..... If you choose that cam you can get away with LS3 valvesprings which is like 55 bucks or so.
As far as mileage goes just replace your oil pump, lifters, timing chain.... don't forget about the trunion kit!! Cheap upgrade!

273k on the motor I wouldn't install a cam. Maybe a set of LT headers, intake and a ported and polished TB, and while still driving the truck start building your motor. JMO

You're going to open up a can of worms trying to install a camshaft on a motor with that mileage.

Cheap as possible and your looking into turbos and supercharges? lol. A good cam will get you the 400 hp your looking for.