The question is also what you need to haul. You can carry a lot with a regular bike and a trailer as shown above. And old kids trailers are plenty and cheap to find on local classifieds. I have Burley Travoy trailer which which I tow behind my bike and use as a shopping cart inside the store and then just hook on to the bike. I have also built my own cargo bike from an older recumbent tandem bike. This one I use for the heavier loads.
There are quite a few different designs and styles of cargo bikes as well: Two wheelers, three wheelers, long tail bikes, Bakfiets, ... and I think everyone has a different demand on what a cargo bike should do.
I would visit a store which focuses on cargo bikes if you have one in the area to check what style would fit your needs. But be aware new ones can be expensive. And used ones can be hard to find depending where you live. I would probably start with a used trailer and check if that fits your need.
Below are one of my bikes with a trailer and the cargo bike I have built.
