Use and learn the search feature for inquiries... or the Tech Tip forum, etc.
The K&N will sound good, but I wouldn't call it a performance mod. AFAIK the Modification Face-Offs that have been performed show only two CAIs provide a performance gain on the Dyno... the Air Hammer and the AFE StageII CAIs. The rest, generally, don't recoup any HP (and I think the K&N is one of those). There were some that seems to flow worse than the stock air box.
Beyond that the cheapest power mod you can do is installation of a 180F Tstat vs. the stock 203F Tstat. For even 10F below about 190F coolant temperature you recoup about 8-10 HP IIRC.
Next (meaning more money) would be an intake manifold spacer although there is some discussion whether those are really beneficial for the plastic intakes of the 5.7L engines.
The next mod would be a Diablo Motorsport Predator tuner... here, again, tunes for the 5.7L are just coming into worthiness, but there is so much more you can adjust... fan settings (to go with the cooler Tstat), shift points, tire sizes (I think)... all of which take some training and experience to do well without risk to the powertrain.
Then... MUCH more money you get into cams, headers, exhaust systems, etc., etc.