We're kind of lucky in this end of things.

We have a full sign and paint shop as a sponsor (3 kids in the family business are on our team!!)

For the lexan parts, we had vinyl stickers made for our sponsors from a plotter as mentioned above.

As for the sides, problem solved. We used very thin tin sheet metal and painted that and attached those on our robot.

Both have proved to be very effective!!

Attached is a pic with the tin painted sides and the vinyl graphics on top for our 2002 robot.

You can't see from this picture, but the actual frame underneath the tin sheet metal had been swiss-cheesed beyond belief.
That's the reason for the tin covering!

Oh, and in case you were wondering, the paint is a ppg candy apple paint, and the swirl effect was done before painting with a harsh wire brush technique (I think!) lol