If i needed to haul cargo that would require a space this large via human power. I might also consider a three wheeled bike with a basket on the back that could be modified slightly to accommodate a larger load well below this price.
I like the three wheeled option for stability with a large load. The trailer option works well for stability too as the trailer has three point contact but add some rolling resistance due to the extra wheel.
I might further be tempted to motorize the three wheeled bike with modified storage basket well under this $899
If this option was sold side by side with his kit I wonder what would sell more...