If you're good at coding but bad at conventional art, you may want to take a look at
http://www.povray.org/ - it's a ray-tracer that uses what is effectively a full-on programming language to specify scenes, and I've used it for making sprites for ships before.
Admittedly, the last time I went tinkering with building sprites for Starsector I got distracted partway through, but here's an example of a (very) work-in-progress ship built using povray:
https://www.silverinsanity.com/~wyvern/Rook.4.png - it's not a perfect match for Starsector's style, but it's close enough that a faction mod using graphics built that way wouldn't look too out of place.
(And, for an example of a ship built in povray that was never intended to be used in Starsector, but still shows some of what you can do with it, see:
https://www.deviantart.com/damurxac/art/The-Nightmare-11766758)
...That all said: you can make an entirely functional mod using nothing but simple colored polygons. It won't
look good*, but that's much easier to address than not having a mod at all.
* With apologies to Harmful Mechanic, whose vector-art (i.e. colored-polygon) ships
do in fact, look good. Though I would argue that they are not, when it comes down to it, 'simple' colored polygons. See:
Magellan Protectorate and
Dassault-Mikoyan Engineering