You searched the FAQ....you don't mean the NissanForums.com FAQ section, do you? Maybe that is why you didn't see any results. Try this link...
http://www.nissanforums.com/search.php?
Type in "cheap mods", or "easy upgrades", or "cheap upgrades" in the Key Word field. I tried it with cheap mods and got some good threads. Example..
http://www.nissanforums.com/showthread.php?t=74218
Just make sure the thread you click on is specific to your vehicle, it will show up in the search results.
Off the top of my head I would suggest you replace the stock air box & filter and replace it with a cone filter. Same principle as the jeep mod you mentioned, to free up the air flow to the engine.
You can also advance the timing to free up horsepower, but you will have to use premium gas to avoid detonation.
Also check the slack on the accelerator cable. This won't increase hp, but if its really loose now you will notice a slight pick up in acceleration if you remove the excess slack.
All these topics have been covered before here, use the search engine to find out more about one particular mod.
That should keep you busy for awhile.
