I would think, at least i hope, that that just over 40k figure is only a placeholder figure while it's in alpha and not reflective of what a Cobra MkIII will cost in the real game.
It was 150k in Elite 2, i think, and i would say there's a good case to make them massively more expensive than this.
We're no longer in a single player universe, and you don't want everyone getting into top-end ships and equipment within a few days of the actual game going live.
I personally think 4 canisters is a little too small, and they should have taken the opportunity to have every ship carry a lot more. Sidewinder 40 tonnes, Cobra MkIII 150 tonnes, etc. But if that's the way it's going to be, that's fine. Maybe a spot of bounty hunting, with the cargo space just for scooping up whatever your kills drop, at least until you get a bigger ship...