I have a 2011 Focus SES. I have put in a K&N cold air intake and have just recently installed an exhaust and I was wondering if there was any other ways to enhance performane without spending too much money
Cams arent really considered expensive, probably as much as your intake or exhaust. Maybe 300 bucks for cams, and you can probably reuse your cam bolts, valvesprings (depending on stage) and gaskets. Very nice boost in horsepower. Also, a custom tune from fswerks or turbo tom, and a header will put you at very good numbers compared to stock.
You could also look into getting some lighter wheels. Decreasing the amount of rotational mass will help your car accelerate quicker and handling slightly better. This also applies to the crank underdrive pulley and the power steering pulley but I don't think that they make lightweight aftermarket pulleys for the 2008+