ComradeShiba Well, you didn't say anything about missiles, so here ya go: my Terrible missile... thing I built as a test ship.

It costs a little under 1 milion credits (about 925,000 ish)
Aftermath:

In before "no missile spam as a new challenge!"
EDIT 2: My very old Solar Class Cruiser won.
Sorta weird fight, the AI piloted my ship quite oddly, using it like a swinging missile cruiser and only using the railguns sometimes. Still, here's the design: (Price is around 1.1 or 1.2 million ish)

Aftermath:

And my Gale Class won which is only 500k! (It was able to keep out of range of everything but the missiles and lasers, and then just picked your ship apart at range. )
Here's the ship design:

Aftermath:
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It should be clear to you now that you really need to redesign your ship... (There's plenty of guides, and you can get help at the building academy thread...)
EDIT 3: Can't seem to replicate that Gale class victory again, so take that with a grain of salt. I will continue to test in the meantime
EDIT 4:
Made a bad broadsider for fun (haven't made one in a long time)
Cost: 1.2 million ish credits

It won with fairly little issue. It just took a while.
Aftermath:

I think we can safely say that your ship needs an upgrade...
This could help you: https://forum.cosmoteer.net/d/7783-cosmoteer-ultimate-ship-design-and-part-guide