here are some that someone posted elsewhere yesterday. I believe he frequents this site as well, so maybe he will chime in as well. As far as I know no one mass produces a good looking "prerunner" bumper.
Loosly used term.
To me a prerunner is a truck, car, or buggy used to prerun a race course. Depending on the sanctioning body (score, bitd, etc...) they have preruns before the race. It gives the drivers a chance to check out the course and make notes, mentally and on GPS systems. Some people like to prerun in a vehicle similar to thier race vehicle, and some people like to do it in luxury. So a prerunner could be anything from a VW bug, to a open wheel buggy, to a full blown luxury prerunner with a/c and crazy amounts of HP and wheel travel, to a stock truck with some bolt on coilovers.
Loosly used it refers to anything that resembles any of this stuff. Some people just build these types of vehicles to go out and have fun in the desert or dunes. So it is not really a prerunner, just a toy.