Some cheap bang for your buck ideas:
LED lighting - a few dollars off Ebay or whatever changes the colors or brightness of the lights. Look for 31mm festoon lighting options
Deckplate mod (not CARB legal) - Cuts a hole in the airbox and replaces with a sealable deck plate for a bit more HP. Search this for instructions
Running board removal - Some people like the look without them. Doesn't look good with some trims and is not desirable by short wives/girlfriends
Clean & wax your 4Runner - Not a "mod" but a clean interior (rent a Rug Doctor) and shiny exterior goes a long way. Especially among the before mentioned wives/girlfriends.