To make a kitless :
You will have to find a nib and learn to make a section around it, realize the first one is not good, make anoth...
You will have to learn to make a closed end barrel and cap, realize your method is so so, make anot...
You will have to make a good drawing with OD, ID, lengths, depths and all, try it, realize it is not good, make another one, try it,realize it is better but not yet good, make ano...
You will have to work on the design to make an elegant pen, try it, realize it is not as good as you wish, try to refine it, make it, realiz...
You will have to learn to thread and make five males and females before making the first decent one.
And I am not speaking of inserting a clip, making the cap postable, learning to deal with resins, and 10 others things.
All that is very possible with a wood lathe, a long jaws mandrel and single start taps.
THEN you may consider buying a collet chuck (a must) or even buying a metal lathe to get a teeny tiny little bit of better accuracy.
You can also spend a lot of $$$ before learning anything, it is very comforting. It is the same as offering a 400$ pen to your 6 year old child who is learning to write. Better offering it when he can write, in my opinion.