I can custom make a 2-wheel or 3-wheel cargo bike to your requirements. They typically use a Cr-Mo rear triangle off a recycled bike, then have stainless steel tube welded on to make the cargo bike frame.
The 3-wheel is fantastic for large & heavy loads being able to carry 150 kg including adults in wheelchairs. It is much larger capacity than European made cargo bikes, and very strong. The front wheels are 26”€¯ downhill mountain bike wheels with 20mm hollow axles which are much stronger than standard 26”€¯ wheels which is important as I have collapsed a couple of standard wheels over the years. The main rotating joint is made from 25mm solid stainless steel so is very strong - also very important as the expensive imported tadpoles can suffer from bearings that slog out. The bin is made from tuffboard which is very durable. the bins is sized to take a wheelchair if required so great for taking adult-sized people for outings. There is a 9 degree tilt on the main rotating joint which means you tend to lean in going around corners which feels more natural. It usually takes a while to get used to the feel of a tadpole, particularly not being able to lean into corners as easily or adjust for road camber. Cost is $2500 for frame, bin, new internal gear hub with coaster brake, new 26 inch 20mm axle front wheels with dual action (one lever) mechanical disc brakes on both front wheels. Bin size is approx. 700mm wide, 1200mm long and 550mm high
The 2-wheel cargo bike is often called a Bakfiets which is Dutch for “cargo bike”. These are great for kids as you can see what they’re up to and converse much more easily than when they’re in a trailer. You can also keep an eye on the loads you put in. This is designed to take a wheelbarrow tray but can be fitted with a deck or custom built bin made from plywood or tuffboard (recycled hay bale wrap). Options are available for wheels and brakes depending on how many gears you want and how much you want to spend. A good option is a new Sturmy Archer 3 speed with coaster brake (back pedal) on the back for $400 extra.
Powder coated frame, spring stand, 2nd hand wheels & brakes (good working order), 7 speed derailleur with friction shifter, and wheelbarrow tray $1200.