Buying the most expensive OXP ship before jumping to the next octant, then immediately selling it, would be simpler.
Even doing that with a core BCC, then switching back to a Cobra Mk III would net about 250k - a good start.
Hmm ... although is there not a loss involved in buying and selling ships? (If there isn't, there should be, I think - the player shouldn't be able to sell a ship for as much as it would cost them to buy.) Of course, at a certain level of wealth, those losses might be relatively trivial, and might outweigh the faff of selling off a holdful of shiny things.
Of course, not everybody flies a Cobra III: if you're in a rarer breed of ship, it might take a lot of searching through the high-tech shipyards before you find another Mk V Whizzo GTi-with-go-faster-stripes for sale. Although if you're flying a Mk V Whizzo etc. then it's probably the most expensive thing out there. And even if you're not, it might take a bit of searching to find a suitably expensive ship on this side of the galactic jump, too.