Using a stock filter and taking out the snorkel that lets in the air into the air box will do about the same as a K&N will. The good thing about K&N or Airraid induction systems is you can use the same filter for practically ever lol.
As far as catback exhaust systems, you are going to get about a 100 different opinion on what you should get, whether it's magnaflow, flowmaster, dynomax etc. You can't really go wrong with any of them it just matters what sound you want.
I myself have a catback magnaflow system that was custom done at a muffler shop. This is probably the best route to go to save money. Cause in the end it will be professionally installed and you are only paying for the piping, muffler, and labor.
-2011 F-150 Lariat: 5.0 "Coyote" V8, 6-spd Auto (6R80E), 3.73 ELocker. White Platinum Metallic Tri-coat.
-1992 Ford Ranger: 4.0L OHV, 5spd (M5OD-R1), 3.27 Open.