I've never heard of underbody cathodes
Those look like neons to me. I've only seen cold cathodes in computers or footwells. LEDS are brighter, though.
I have cold cathode footwells, you can get them in dual 12" packs at CompUSA for $10. Blue, Red, Green, Yellow and UV only though. I've heard good things about El Wire, so I would go with it. I've never purchased from their website.