Sorry for the necro, but I've just started using starliners as my principle cargo hauler myself (after overlooking them)
Sure supply cost sucks, but it isn't that much of a concern to me anymore. (at least not from a cost perspective; running out can still be a concern
).
At burn 9, the "Cargo capacity per fleet slot" is unmatched, same burn efficiency as buffalo too, yet a much more efficient fuel transport, so there's no need to drag a Phaeton around with you.
As having a large fleet cargo capacity increases the likelihood of encountering large courier missions (which can be disgustingly profitable), it makes sense to run around with a fast cargo and huge cargo hauling fleet all the time.
The only significant downsides are:
- sensor profile is double that of the buffalo
- you don't get shielded cargo holds.
- CR recovery cost is 4 times higher (this one actually bites quite hard; emergency burn becomes insanely expensive)
:edit:
Also, fill all that personnel space with additional crew, and you'll never again waste any crew XP - creating an additional (fairly lucrative) revenue source.