Yes ebay has some really bright leds for next to nothing. You can get bulk packs for ultra cheap as well.
You just need to wire them up and use a good resistor. Trial and error for a newb, but its real easy. So get a few.
You can also get an extension and cut into that so you can plug it in and out without cutting into your exsisting wires. You can also wire it to a seperate AA battery. They dont need really any power to run. The larger the heavier in the car...so stick with that size or possibly smaller.
Just single cell holder and you can even just glue this all to the body if you intend on making headlights and tail lights.
But normally its only good to do when you already masked off the body over the headlights and tailights so it can shine through nicely. At least for the headlight.