hi...you can replace just the antenna part
i did it with my shogun when i had it...simple job aswell. if i remember correctly the antenna part was about 18 pounds from mitsi......i think ( was along time ago now :lol: ).
to replace.
make sure stereo is turned off and antenna is as far down as possible
undo the chrome nut on the bottom of antenna .....where is meets the car
now turn radio on so antenna extends. it will keep coming out
now get new one and push into hole.. turn the radio off and wait for it to pull the new atenna in. do up the nut again.
one thing to watch for when removing it is when it comes out watch the plastic strip inside. see which way it is facing. when putting the new one in try and make sure it goes in the same way
i hope this helps abit. if not give me a shout