The reason its cheap is cos i actually bypass Jaycar and go to Digitech. It does still ahve the warranty on it, but it has to come back to me and I'd have to sort it out for you. Usually its a no questions asked replacement policy on low value items... but obviously if it looks like its been crushed by a car it'd look a lil sus.
Failing that, I've found the simplest way was to buy one from jaycar, chuck the broken one in, and return it to get your cash back bit cheeky, but when you need a replacement in a hurry, its the easiest way. Not that I endorse this officially
When my mates go 4WD'ing, we just hook up the 3W cb to a external omnidirectional antenna, and it boosts the signal clarity greatly... one of the joys of a standardised antenna plug. Digitech also sells a 8db signal booster antenna with a magnetic base, which might be better than the supplied one if you wanna upgrade.