The thing I don't think I recall hearing is weight or volume per load.
Your viable options could change quite a bit with variations in those.

Anyhow, since you had initially proposed a bicycle, I'd say you'd be
hard-pressed to improve on the cost-efficiency of a moped. Taking the
Eaton/Peterbilt approach, if you were able to drive your per-trip
operational cost down to $.05 by virtue of, say, $100K in development
costs, it would take a long time to amortize that start-up cost.

Do you have a business plan so you know your break-even point?

--
St. John, not ready to write a check just yet