Cams are a great bang for buck but they are in no sense cheap. Taking the example of the hitech stage II's they are $600 plus the install and the necessary dyno tune.... so you are looking at over $1k easy.
Hitech recommends springs if your stang is over 100k miles. I did my cams w/ the stock springs since I have ~70k miles. I'll tell you from first hand experience that there is significantly more valvetrain noise, if I were to do it again I would probably do springs even with the additional cost.
They also advertise that their cams don't require degreeing, this is not the case however. These cams favor the intake side and there are some reports of piston to valve clearance problems on the intake side- each side of our 4.6L motors can be slightly off from the factory because the stock cams allow this- but w/ aftermarket cams you don't have as much clearance------***make sure you degree any set of new cams.
Other than that last scare paragraph I love my hitech stage II's. No loss of power down low, solid gains in the midrange and top end. A nice flat torque curve, I couldn't ask for much more. I put down 290rwhp on a mustang dyno which should be good for 300+ on a dynojet. But that is in addition to full boltons. With the cams my nitto 555's have a tough time keeping up in 1st and 2nd.
Hitech sells blower/nitrous cams and many other companies do as well. Most NA cams will work fine with nitrous too, just make sure you tune. Take a look at the stage II cams such as the comp 270's, MHS, and hitech just to name a few.
Learn a little about the specs on the cams, watch youtube videos, and figure out what you want from the cams (power, sound, driveability). The majority of the sound that you get from your cams depends on your current exhaust setup / future exhaust setup. An offroad midpipe will get you the most lope. Also don't get the biggest cam out there, really a stage III cam is not for stock heads / daily driven car, you end up losing too much power in the low rpm range.