$/Lumen is the magic number. Hot-wire lamps do really well (250w halogen worklight bulb costs $2, and cranks out 5k Lumens.) and LED's really suck. This
BEAST is almost $70, and cranks out roughly the same light output.
Of course, you can just buy 24v halogens- a LED needs electronics to run safely- cheap lamps use a resistor to limit current, while bigger/better ones use a switch-mode driver. That Bridgelux LED array uses only 50w, but very few driver circuits can handle that. Then you have to keep the LED under it's safe temperature, usually in the neighborhood of 140F. That Bridgelux would need to be stuck to a huge heatsink, OUTSIDE the engine compartment, to be safe. Lots more engineering than a Hot-wire that'll handle 4-500F, and voltage from 20-30v.
Replace your front bumper with an aluminum I-beam, stick a few of those huge LED's on it with an optic, and there you go!