Take Engine Components from Houston to LA and Polymers back. Should get you like 45k round trip.

tag

Planet Houston (Texas) => Montezuma Base (Cortez)
sell Optronics: 770
profit: 210
buy Engine Compontens: 600

Montezuma Base (Cortez) => Planet Manhatten (New York)
sell Engine Components: 1424
profit: 824
buy Cardamine: 840

Planet Manhatten (New York) => Fort Bush (New York)
sell Cardamine: 1500
profit: 660

Fort Bush (New York) => Planet Houston (Texas)
buy Optronics: 560


overall profit: 1694 per cargo unit


you gotta be neutral to the rogues to do this trip.
destroy some cargo depots surrounding manhatten (fly to the right after launching from there and turn your loot targetting on) to achieve this.

Rogues are just a pain to get to neutral.

not really.
kill some cargo depots as mentioned, and theyre neutral.

that is ofc if u didnt kill tons of them before doing so

Cortez is, technically, a border world, and not Liberty space

Unless I'm mistaking you can't buy drugs on manhattan - you must refer to a rogue base nearby ?

My experience is, that there a lots of cops in the new york system - makes hauling drugs a bit of a hassle.

sure, u cant buy cardamine on manhatten.
but if u look closely,

Montezuma Base (Cortez) => Planet Manhatten (New York)
sell Engine Components: 1424
profit: 824
buy Cardamine: 840

means that u have to buy cardamine on the montezuma base and not on manhatten.

and if u keep on afterburning into the tradelanes u wont have any problems with the police.
afterburn and kill your engine ("z" key) then if your afterburner isnt strong enough to keep 300 over long times. press F3 only when u almost already entered the tradelane.
its all about speed

and yes, technically cortez isnt liberty space, but its only 1 jump to it, so its very very close