Where did you find out that one oxygen in freelancer is a ton of it?
Starflier is like a car, you can get may be two people into it and some bags in cargo hold. (yes carring 20 prisoners or 4 tanks in starflier is just another proof how disco is developed by popular "look from window and write what gets on your mind first" system)
On planets fighters and freighters are seen flying between skyscrapers like in various sci-fi movies, so in my oppinion freelancer developers meant small ships would be as usuall as cars. Of course some atmospheric-only vehicles exist too but its like small motobikes.
In freelancer singleplayer was mentioned that its not enough to have fighter/freighter to be able to fly in another system you also need access codes, unless your pirate, intersystem traffic is highly controlled by owners of jumpgates. So unless people live by trading between systems they usually dont have access to jumpgates and have to use public transport companies for such travel. But people who need it can buy it so we can assume that buying freighter and registry for it would be something like in our world ie. most would probably take some loan for it, but it would be in their power to pay it back.
avg person could make in my oppinion some 30000 sirius credits a month varrying from system to system from house to house.
Naturally pirates would be completely different as what they dont steal they will never have, unless they would also take some other means to make money, like gambling on freeports all day long:))
