Don't forget, with the recent changes, all haulers are incredibly easy to train into, so I've swapped from Mammoths to Iteron Vs.

Train Gallente Industrial I and you can be sat in an Itty5 in 33m or less.
With about 15h training, to get expanded cargohold IIs and cargohold optimization rigs installed, you have a 32,284m3 hauler.
Train Gallente Ind to 3, another 17h training, and you are hauling over 35,358m3.

A similarly fitted (Minmatar Ind 3) Mammoth only hauls 25,999m3.

Jita prices are around 2m for a Mammoth and only 2.4m for the Itty5.