Here's a TL9 Spru-Can, built under High Guard
Note it's TL9, so I limited it to pulling 3 gees (compensator tech and all that). It's jump-1, but has fuel for a second jump. It's lightly armed, with a 100dton PAW and a 100 dton missile bay, plus some token sand and missile launchers. Agility 3 and armor 4 mean it's a ship that might stay alive long enough to get away when fighting something with a spinal mount ... but it'll be a terror to any civilian ships, as the combination of a 100dton PAW bay and armor 4 mean bad bad things if it fights civilian ships.
217 dtons of cargo means it can stay on patrol for a while, and it's bang on the expected budget of MCr1 per dton for a military ship.
Assuming Cr90 naval taxes per citizen on a TL9 world, that means MCr90 per million citizens, so with a GCr3 build cost, a planet with 100m citizens could happily afford several.