Cargo bikes are obscenely expensive (the cheapest I've seen was double what I paid for my car) ... what I do see being used here sometimes are old rusty mountain bikes with homebuilt trailers (dexian, plywood, two wheels from a kid's bike), which seems like a more sensible solution given the trailer can be swapped between bikes or even reconfigured depending on needs
A partial car substitute? Trek’s new cargo bike, reviewed ( arstechnica.com )