EBAY and get a used one...
My fill rig cost me just over £30 think it was £15 for the CB, 12 ish for a 6ft whip with gutter mount, and £3 for the cable (still annoyed, cos I know ive got 50ft of the stuff somwhere) mines mounted on the bumper, not had to tighten it up yet, used a bit of threadlock on the mounting screws when I put it on though.
Just cleaned a bit of paint off where the screws bite in, got a really good earth, range is more than I'll ever need out laning.