i've got the powered setup but don't need it to work up and down.

the telescoping part broke off leaving the threaded/hex head screwed in on the fender, with a two inch stub going down in the hollow shaft.

are the antennas advertised at various places, the hex nut/threaded part with the telescoping antenna what you get when you replace the mast or is it something else altogether.

 

I don't know what you've seem advertised, but generally you'd replace the whole assembly. A good replacement is about $100. I think you might be able to order just the mast, but you'll have to know the make and model of the antenna.

If you don't need a power antenna, you can get an antenna that you raise and lower manually a lot cheaper.