I started with a 1/4" wood dowel ($1)
A pack of assorted vinyl vacuum end caps ($2.50)
1/4" vinyl hose from Home Depot ($3)
I slipped my dowel down into the radio to the desired height, marked that and cut it. It fits in the radio snug and won't fall out.
Cut my clear hose down and added the vacuum cap. From here you can dip it in the Plasti-Dip or, what I did next since I had some laying around is I added some heat shrink to the wood and clear tube. Just to make it a bit beefier. You don't have to do this. I was just playing around.
This stuff in black.
I let it dry for 30 minutes and then flipped it over, I put a bit of water on the tip of my finger and tapped the pointed end down and then let it set upright for another hour.
Of course, I couldn't wait.. So I tried it on the radio. Not too shabby for a project that took a few hours.
All said and done this project cost me $17. So not as cheap as getting one off of eBay. But, if you need to build three or four then suddenly this is the better way to go. I am planning on one day making a MT500 kit in resin, so having an antenna that is my own creation is important to me.
Hope this helps!