According to George Dyson
's book, the pulse unit for a 30 foot diameter ship was 1 kiloton and weighed a little over 300 pounds. 2,000-3,000 of these would have been needed to get to Mars and back. The Orion team explored a wide range of possible ship sizes and concluded that a 400 meter diameter vessel would be the largest feasible size for lift-off from the Earth's surface. This lift-off would be possible with hydrogen bomb
There is a quote by Freeman Dyson in the book that mentions a calculated 5 cents per pound of payload (at 1960s era prices) for a 1,000,000 ton ship powered by a few thousand megaton H-bombs.