Dear Jerra,
as it looks like you're completly new not only to Crossfire, but also to Freelancer, otherwise you would know, that EVERY colony in Sirius, Bretonia, Kusari, Rheinland and Liberty have prisons, but you haven't found the other prisons by now.
They are here:
Kusari: Shikogusystem, from Deshimastation in direction of the battleship behind the battleship, just fly for a few seconds and you will see Fuchu-prison.
Bretonia: Manchestersystem, from Sheffieldstation take a course righthand between the planet and the sun, the asteroidfield on your left, it takes quite a time, folloe the patrolpathes down south, the prisonstation is in a dense MINEfield but there are some nav-bouies, fly inbetween and dock.
Rheinland: Hamburgsystem, when at the gate to New Berlin take a course through the asteroidfield on the leftside (on your navmap) to the planet you can see, fly straight into the direction of this planet, it's some way, similar to Manchester, on the way you will additionally find a jumphole to New Berlin, when you've almost reached the planet the prisonstation "Vierlande" will show up, as additional help follow again the patrolmap paths.
If you're not familiar with "spoiler" see your pm.
From the price I assume you are flying the Trailblazer" now. With a bit of good flying a ship completly capable to finish the story line.
For a decent weaponry you might want to check the spoiler forum. There you can find a link to a list with all the original wrecks (and their loot-weaponry:D ).
General tip: EXPLORE
If you have now time until you got the 500k creds together for advancing in the story, take that time to explore.
My strategy on this was killing Xenos, LOTS of Xenos until everybodyelse was neutral white on my reputationlist. Also helpfull, become neutral to Outcast and Red Hessians and chase corsairs for better pods in the Omegasystems. For the storyline you don't need the corsairs other than paying your bills as bounty.
And the outcast home system (find it by yourself, it's not to difficult) is a nice place to rest.
When you're finished with singleplay come to the server-universe. The NPCs lightfighters are a nuisance in the beginning, but there are MUCH MORE TO KILL [SIZE=1]just for the fun, you know.[/SIZE]