Peruse this category for a review of bikes capable of handling weight in addition to the rider.
https://electricbikereview.com/forums/threads/best-electric-cargo-bikes-for-2020.32707/
Heaviest duty steel frame cargo bike with lots of hanger points comes from Surly.
Cheapest non-powered stretch cargo bike is the envoy mongoose, which see under kits & conversions.
Your size matters including your weight, length of arms & legs. that determines what size frame & wheels you will best suit you. Type of surface matters. Fluffy powder snow, beach sand, fat tires >3" are in order. Ice, large clearances for fenders & spikes are in order. Pavement gravel grass mud, I find 2.1" x 26" tires adequate, with knobby tires. Maximum grade matters. I carry 80 lb cargo, 94 lb bike+tools, 170 lb me, up 15% grades with a 500 W geared hub motor. (Mac12) If that motor fails (ebikeling 1300 w one did at 4500 miles) I can ride it home self powered. My stretch frame can carry up to 12' long light loads over the aluminum rear rack + hanger from the handlebar. Carried home some abandoned 3/4"x 10' conduit last week.
Mid drives are better at climbing rocks or grades >15%. They also strand you if something goes wrong in motor or chain. Mid drives wear out chains twice to four times as fast as hub drives. Especially chains thinner than 8 speed rear cluster. If your route climbs >1000' in 25 minutes, a geared hub motor will short a winding from the heat. Not a problem in the midwest; I cover 77 hills in 27 miles, but short rollers.
Bikes under $2000 come with kiddie grade shifters, cables, spokes & chains. The brand you chose has >30 complaints of loose spokes on known problems thread. I've broken the axle of a 6 speed shimano rear when I weighed 190. I had a 7 speed shimano rear come unscrewed and drop the balls, making me walk. Stupid design for kids that ride 200 miles in the life of the bike. Cheap shifters & cables, like the shimano & sun 7 speeds, require frequent adjustment. I've adjusted the SRAM on my yubabike once in 6000 miles. Only the stop screw. Real steel cables don't stretch. That bike cost $1500 with 2 panniers, front basket, 2 leg stand, free freight. I added $221 in front hub motor & $630 battery, $30 aluminum & screws. That motor wore out in 4500 miles, now I have $730 Mac12. Took 2 afternoons to swap drives, 1 building a new mount for the controller. Try swapping a defective mid drive that fast. Hub motors do need cover screws tightened occasionally. Don't buy a direct drive hub motor for anything but flat level fast city riding.
You probably can't build a bike cheaper than you can buy one now. Exception, my yuba bodaboda came unpowered with 24 speed sprockets, triple front crank, which you can't buy pre-built. I then added a front hub motor, which you also can't buy installed. Front hub motor can throw one if rider powers through ice, slick rock, wet wood, muddy steel plates, or other low traction situations. Front drive would be a big attraction to tort lawyers in US market. You can't buy a bike with one. I just turn the power off in slick situations. I walk bike on really slick situations. Front hub motor & battery balances the rear cargo better, makes the bike easier to push over the step into my garage.
Happy shopping & cruising the woods & fields.