Actually, if all you're looking for is "effects" lighting that isn't linked to what the robot is doing, you can just power the LEDs (and arduino) through a single relay (or half a spike), and turn it on as part of your startup sequence. If you actually want to control it from the driver station or 'Rio via an arduino, you will need one of these comms paths.
As another alternative, you can use a much less expensive relay than the spike to turn on low-current custom circuits, something like this:
http://www.miniinthebox.com/4-channe...caAnA u8P8HAQ Since it has a 5V input, you can switch it directly from a DIO port on the 'Rio. If you have enough DIO ports to spare and boards like that one, you can just program all of your LED strings from the roboRio. If you have three PWM ports to spare, you could maybe even do those color-changing strips.