I've got the current "almost 5.1" PDF version of the Traveller 5
rules.  I've been playing around with the ship design rules.

What has 65.2 Dtons of cargo space, Jump 2/ 2 G accel, a crew of 4 and
only cost 7 MCr? The cheapest possible ship in Traveller 5, or what I
think is the cheapest.

With weapons, some computer automation and less chance of crew
insanity it has 41.7 Dtons of Cargo space and cost 17.0 MCr.

Full design notes can be seen here http://3rdimperium.org/?p=999