$30 for an led and bit of metal, bloody norah...
Tricky though, if you do alot of bashing then your best bet would be for some thing like a simple front+rear set, and mount them on the front and rear bulks (with voodoo magic until I think of something better):
http://cgi.ebay.com/eBayISAPI.dll?Vi...m=200348782399
Something like an L shaped bracket that mounts where the bumper mounts normally go, then drill a hole so the led holder thing can screw in place. JUst cut off whatever power connector they have, and wire them to the pico switch (single + and - leads there should be). Then wire the power connector to the picoswitch in the proper location (little screw terminals probably) and add a suitable battery, probably a 9v item that can tuck away neatly and securely.