It's an SCTA/USFRA requirement -- you won't pass tech without one. I'm pretty sure the SCTA rulebook (which USFRA follows) now requires a dash-mounted CB, too -- not a handheld.
At World of Speed today we've had to turn away a few racers that didn't have a CB in their support vehicles. Good thing that the Pilot truckstop here has a Midland CB, full power and dash mount and all -- for $40. I don't know the price of an antenna, but it probably gets the total to $75 or so.Get a real antenna -- not a little rubber ducky-type. The longer the better is absolutely true in CB --= a magnet-mount with a 3 1/2-foot whip, on the roof, will make a big difference vs. that little 10-inch rubber one.
The requirement is there for good reason -- so the tower can tell the support vehicle of important thinmgs like "Your driver has turned off at the 2 1/2 mile mark -- go fetch him" or "Hey, grey pickup going past the pits -- it's a 25-mph zone. Slow down!"