@agegamon@ada there are also trikes in that price range like from lectric and radpower, which could be a good option for a lot of people but your top speed on that is more like 12 even downhill, so you don't tip over. If you're going slower, the trike can be easier to manage a big load, but bakfiets are great at 12-20mph 30 if you like wind.
Compared to used car prices, unfortunately there are not many used cargo bikes. I think the cheapest new option would be like the unfinished project I'm riding, which is fine on small hills or if you don't mind working hard sometimes, top assist speed 15mph (+~$500 more = moarโก)
$3k acoustic supercargo, 440lb max load yubabikes.com/cargobikestore/supercargo/
$570 tiny 250W 190Wh #eBike wheel โ torque arm hilltopperbikes.com/product/sprinter-12-mile-24v-electric-bike-kit-copy/
@markstos@dx@agegamon ๐ this kind of thing has me thinking I should just have the kid crank/treddle a generator rather than try to get their power there mechanically